Method of inserting viral DNA into plant material

ABSTRACT

The present invention relates to a novel method of inserting viral DNA, which optionally may contain cargo-DNA, into plants or viable parts thereof, but preferably into plants of the monocotyledon class, and most preferably into plants of the family Gramineae, using suitable transfer microorganisms. Further comprised by the invention are recombinant DNA, plasmid and vector molecules suitably adapted to the specific conditions of the process according to the invention and the transgenic plant products obtainable in accordance with the said process.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a division of application Ser. No. 08/272,958, filed Jul. 11,1994, which issued as U.S. Pat. No. 5,569,597 on Oct. 29, 1996, which isa continuation of application Ser. No. 07/966,268, filed Oct. 26, 1992,now U.S. Pat. No. 5,290,938, which is a continuation of application Ser.No. 07/497,799, filed Mar. 22, 1990, now abandoned, which is acontinuation of application Ser. No. 07/118,094, filed Nov. 5, 1987, nowabandoned, and a continuation of Ser. No. 07/798,859 filed Nov. 22,1991, now abandoned, which is a continuation of application Ser. No.07/526,949 filed May 22, 1990, now abandoned, which is a continuation ofapplication Ser. No. 07/211,080 filed Jun. 21, 1988, now abandoned,which is a continuation of application Ser. No. 06/859,682 filed May 5,1986, now abandoned.

The present invention relates to a novel method of inserting viral DNA,which optionally may contain cargo-DNA, into plants or viable partsthereof, but preferably into plants of the monocotyledon class, and mostpreferably into plants of the family Gramineae, using suitable transfermicroorganisms. Further comprised by the invention are recombinant DNA,plasmid and vector molecules suitably adapted to the specific conditionsof the process according to the invention and the transgenic plantproducts obtainable in accordance with the said process.

In view of the rapid increase in world population and the associatedgreater need for food-stuffs and raw materials, increasing the yield ofuseful plants and also increased extraction of plant contents, that isto say progress in the field of foodstuffs and medicines, is one of themost urgent tasks of biological and biotechnological research. In thisconnection, for example the following should be mentioned as essentialaspects: increasing the resistance of useful plants to diseases andpests or to unfavourable soil conditions, increasing resistance toplant-protecting agents such as insecticides, herbicides, fungicides andbactericides, and beneficially modifying the nutrient content or theyield of plants. Such desirable effects could in general be broughtabout by induction or increased formation of protective substances,valuable proteins or toxins and by interventions in the regulatorysystem of plant metabolism. Influencing the plant genotype appropriatelycan be effected, for example, by transferring new genes into wholeplants or into plant cells.

It has already proved possible in many cases to insert selected DNAfragments into viral DNA and then, together with the virus, to introducethem into another organism. Although most plant viruses are transmittedunder natural conditions by insects that feed on infected and uninfectedplants, thereby causing fresh infection of plants, this route is tooinconvenient and difficult to control to achieve a selective andsystematic transmission of viruses. Thus, for example, specially bredinsect populations would be required for such a method under containedconditions. In addition, it would be very difficult to achieve acontrolled virus infection, especially of large amounts of plantmaterial.

The mechanical inoculation of leaves with viruses, the method so faremployed in genetic engineering, is of only limited applicability, ascloned viral DNA is commonly believed to be non-infectious.

Although it is possible to clone and study in bacteria a variety oftypes of viral genomes, for example single stranded DNA viruses which amobtained by cloning double-stranded DNA forms [Mullineaux, P. M. et al,1984], many viruses that are cloned in bacteria cannot be reintroducedinto plants or used for infecting plants. The use of methods such as invitro mutagenesis and recombinant DNA technology are therefore ruled outin basic studies as well as for exploiting such viruses as carriers ofselected foreign DNA. Such problems do not arise when using the methodof this invention as set forth hereinbelow.

Prior to the present invention there have been only a few reportsconcerning the introduction of cloned viral DNA into plant cells.

Howell et al (1980), for example, describe infection of turnip plants bycloned CaMV DNA. It is specifically emphasized in the said referencethat the cloned viral DNA must be excised from the recombinant plasmidbefore it is capable of infecting the turnip plants. Lebeurier et al(1982) demonstrate that a cloned tandem dimer of CaMV DNA with a partialdeletion is infectious in a plant assay. The viral genome was inoculatedas part of a pBR322 double-stranded DNA plasmid by artificial leafinoculation. Lebeurier et al do not teach introduction of a tandemlyduplicated CaMV genome into the plant cell as part of an AgrobacteriumTi-plasmid using the Agrobacterium transformation system.

Cress et al (1983) demonstrate that dimeric PSTV cDNA is infectious in aplant assay when inoculated by artificial means as part of a recombinantbacterial plasmid. Again, Cress et al do not teach use of theAgrobacterium system as an alternative route for delivering the viralDNA into the plant cell.

Prior to the present invention the only mentioning of viral DNA inconnection with the Agrobacterium transformation system can be found inU.S. Pat. No. 4,536,475 [Anderson] and Shewmaker et al (1985).

Anderson [U.S. Pat. No. 4,536,475] discloses a variety of recombinantplasmid molecules which comprise a bacterial plasmid into which areligated the border sequences from the T-DNA regions of the Ti-plasmid ofAgrobacterium tumefaciens. Anderson teach that the CaMV DNA can beemployed as a DNA source of an eucaryotic origin of replication, whichwas considered helpful in increasing the opportunity for integration ofthe introduced DNA to occur.

Accordingly, Anderson disclose CaMV DNA sequences that are situatedoutside of the the T-DNA and thus have not been assigned for theintroduction into the plant cell's genome.

Shewmaker et al (1985), on the other side, describe experiments in whicha full-length copy of CaMV is introduced into plant cells using aTi-plasmid of Agrobacterium tumefaciens. However, within the geneticconstruct used by Shewmaker et al (1985) the full-length viral genome isbroken in two places and could thus not give rise to viral infection.Accordingly, by the above experiments Shewmaker et al (1985) were onlyable to demonstrate that the introduced CaMV genome gave rise to twopolyadenylation transcripts. The teaching of Shewmaker et al is thusconfined to a showing that the two major promoters of the CaMV genomeare supposedly able to function in plant cells.

The above short discussion of the cited references shows that the priorart teaches essentially two different experimental approaches.

The objective of the main approach, which is represented by theLebeurier et al (1982), the Cress et al (1983), and the Howell et al(1980) reference, is to develop a plant viral transformation systemwhich shall make use of the specific properties of infectious plantvirus particles. To achieve this objective, either the cloned viral DNAis excised from the recombinant bacterial plasmid prior to infecting theplant material [Howell et al (1980); Cress et al (1983)], or the wholerecombinant plasmid containing duplicated vial copies, which proved ableto become recombined out in the plant cell, is introduced into the plantby artificial means [Lebeurier et al (1983)].

However, using the above roughly sketched experimental approach fordeveloping a virus-based plant transformation system would not help toovercome the disadvantages which are involved in a pure viral vectorsystem.

The second experimental approach, which is represented by Shewmaker etal (1983) and by U.S. Pat. No. 4,536,475 [Anderson], relates to studiesfor establishing novel, improved

Ti-plasmid based vector systems, for example by use of plant viralregulatory DNA sequences, such as the two CaMV promoters described inShewmaker et al (1983), or of the CaMV replication origin as describedin U.S. Pat. No. 4,536,475 [Anderson].

Neither Shewmaker et al (1983) nor U.S. Pat. No. 4,536,475 [Anderson]teach the introduction of a complete, intact viral genome, which iscapable of giving rise to a functional virus particle in the transformedplant.

Thus, it was one of the main objectives of the instant invention toprovide a method for reintroducing cloned viral DNA, that is normallynot infectious upon mechanical inoculation of plant material, intoplants.

Within the scope of the present invention it was surprisingly found thatin order to achieve this object the two principle experimentalapproaches discussed hereinbefore can be suitably combined By taking acombination of selected and rather simple measures, parts of which werealready known, it is possible to accomplish the transfer of a functionalviral DNA to a plant.

This finding was very surprising, since it was long known thatAgrobacterium-mediated DNA delivery is a very complex process involvingcomplex DNA protein interactions, both on the bacterial and on the plantlevel, which govern transmission of T-DNA to plant cells. So it is, forexample, still not known what the T-DNA intermediates look like.

Agrobacterium carries three genetic components that are required forplant cell transformation. The T-DNA is the mobile DNA element that,unlike other transposable elements, does not encode the products thatmediate its transfer. Instead, the Ti plasmid virulence region providesmost of the trans-acting products for the DNA transfer to the plant. Thethird component of the T-DNA transfer process resides in theAgrobacterium chromosome.

The activation of the vir gene expression is followed by severaldramatic changes to the T-DNA element on the Ti plasmid that ultimatelyresult in its transfer to the plant cell.

Unlike DNA transfer between bacteria during conjugation, T-DNA must becapable of penetrating the plant cell membrane, localizing andeventually penetrating the nuclear membrane. For this purpose the T-DNAintermediate is expected to have a specific structure, the nature ofwhich is not yet known. A considerable and meanwhile well recognizedsuggestion in this respect is that single stranded T-DNA intermediatesare involved in the T-DNA transfer process [Zambryski A, (1988)], whichwould not leave any of the known options for the viral DNA to becomereleased.

Therefore, owing to the many imponderabilities involved in DNA deliveryvia Agrobacterium it was very surprising to find that the conceptenvisaged by the present invention did actually work.

In particular, the present invention relates to a novel method ofintroducing cloned viral DNA or functional equivalents thereof, that arenormally not infectious upon mechanical inoculation of plants, intoplant material of plants that are naturally amenable, or, if not, aremade amenable artificially, to transformation by a transfermicroorganism such as, for example, a transfer microorganism of thegenus Agrobacterium, or viable parts thereof such as, for example, plantcell culture cells, which method comprises essentially the followingprocedural steps:

a) inserting cloned viral DNA or functional parts thereof, thatpreferably are capable of giving rise to a systemic infection, andoptionally may contain cargo DNA, into a T-replicon, for example aTi-plasmid or Ri-plasmid of an Agrobacterium, in the vicinity of one ormore T-DNA border sequences, the distance between said viral DNA and theT-DNA sequence or sequences being chosen such that viral DNA, includingany cargo DNA present, is transferred to plant material;

b) introducing the replicon into a transfer microorganism, for example amicroorganism of the genus Agrobacterium; and

c) infecting plant material with the transfer microorganism that hasbeen modified in accordance with b).

This method ensures that, after induction of the microbial functionsthat promote the transfer of the plasmid DNA to plants, the inserted DNAis also transferred, including any cargo DNA that may be present. Thetransformed plant material so obtained can be regenerated to completelytransformed plants.

The said induction process described in detail below may, on the onehand, be triggered by the plant itself, if suitable culturing andapplication conditions are applied, the plant being stimulated therebyto synthesize the said inducers itself; or alternatively synthetic ornatural inducers such as those provided in formulae I and Ia may beadded to the culture medium individually or in combination in a suitableconcentration.

In applying the method according to the invention it was furthersurprisingly found that not only those plants known to be host plants ofAgrobacterium could be transformed by the method according to theinvention, but also plants belonging to the monocotyledon class and hereespecially plants of the family Gramineae, which prior to the presentinveniton were commonly believed to be insusceptible to an Agrobacteriuminfection.

The greatest problem in using recombinant DNA technology in plants fromthe monocotyledon group resides in the lack of suitable transfermicroorganisms, with the aid of which transformation frequencies thatare sufficiently high for practical application can be achieved andwhich could thus be used as auxiliaries for a specifically directedinsertion into the plant genome. Agrobacterium tumefaciens, for example,one of the most used transfer microorganisms for inserting geneticmaterial into plants, is excellently suitable for genetic manipulationof numerous dicotyledonous plants, but so far it has not been possibleto achieve correspondingly satisfactory results with representatives ofmonocotyledons, especially monocotyledonous cultivated plants since,from the monocotyledon class, so far only a few selected families areknown that respond to infection with Agrobacterium tumefaciens and thus,at least theoretically, might be open to genetic manipulation. Thesefamilies are, however, from the point of view of agricultural economics,insignificant marginal groups which could at most, be of importance asmodel plants. [DeCleene M., 1985; Hernalsteens J. P. et al, 1984;Hooykaas-Van Slogteren G. M. S. et al, 1984; Graves A. C. F. and GoldmanS. L., 1987].

It is precisely the Gramineae family, however, which includes thecultivated plants that are the most important from the point of view ofagricultural economics including our most important types of cereal,such as, for example, wheat, barley, rye, oats, maize, rice, millet,inter alia, which are of particular exonomic interest, so that thedevelopment of processes that make it possible, irrespective of theabove-mentioned limitations, also to make Gramineae representatives opento direct genetic modification must be regarded as an urgent problem.

The present invention thus preferably relates to a method of introducingcloned viral DNA, that optionally may contain cargo-DNA and is normallynot infectious upon mechanical inoculation of plant material, into wholeplants of the Gramineae family or into viable parts thereof.

Contrary to all expectations, in the course of the investigationscarried out within the scope of this invention it has surprisingly beenshown that in using the method according to the invention it is now alsopossible for plants from the monocotyledon group, but especially fromthe family Gramineae, to become transformed in a specifically directedmanner using certain transfer microorganisms such as, for example,Agrobacterium tumefaciens, that is to say, now also importantrepresentatives from the monocotyledon group, especially cultivatedplants belonging to the Gramineae family, are accessible to infection bythe said transfer microorganism.

The plants transformed in this manner can be identified by suitablemethods of verification. There has proved especially suitable for thisthe use of virus genomes of plant-pathogenic viruses, such as, forexample, Maize Streak Virus (MSV), by means of which successfultransformations can be verified very efficiently by way of the diseasesymptoms that appear.

However, within the scope of the present invention it was nowsurprisingly found, that by applying a combination of suitableprocedural measures, involving, for example, the use of a suitable plantmaterial and a suitable inoculation site for the DNA probe to beintroduced, it is possible to achieve that high a transformationfrequency, that it would no longer be necessary to rely on diseasesymptoms in order to verify a positive transformation event This wouldmean, however, that the Agrobacterium transformation system can now beapplied directly to graminaceous monocots without any viral DNA beinginvolved.

Attention is thus drawn especially to the broadening of the hostspectrum of Agrobacterium tumefaciens to include Gramineae, by means ofwhich even in representatives of this family a direct and specificallytargeted manipulation of the genome is now possible.

In one of its aspects the present invention therefore relates to aprocess for inserting genetic material into monocotyledonous plants ofthe family Gramineae or viable parts thereof, wherein a transfermicroorganism that contains the genetic material in a transportable formis made usable for infection of monocotyledons by employing suitableculturing and application methods that make possible the induction ofthe virulence gene functions of the transfer microorganism, and whereinmonocotyledonous plants or viable parts thereof are infected therewith.

Further comprised by the invention are recombinant DNA, plasmid andvector molecules suitably adapted to the specific conditions of theprocess according to the invention and the transgenic plant productsobtainable in accordance with the said process.

The present invention also relates to the use of vector systems such asthose described above under c), and especially of novel vector systemssuch as, for example, bacteria of the strain Agrobacterium tumefaciensA136 (pTiBo542, pEAP18::Ca305) and Agrobacterium tumefaciens A136(pTiBo542, pEA1) Agrobacterium tumefaciens (Rif^(R)) C58 (pTi C58; pEAP200) and also Agrobacterium tumefaciens C58 (pTiC58; pEAP37), C58(pTiC58; pEAP29), C58 (pTiC58; pEAP40) and also C58 (pTiC58, MSV 109)for the controlled transformation of plants or viable parts thereof.

To ensure a clear and uniform understanding of the description and theclaims and also of the scope the said claims are to have, the followingare given as definitions within the scope of the present invention.

Transfer-microorganism

Microorganism that can transfer a part of its DNA into plant material(for example Agrobacterium tumefaciens).

T-replicon

A replicon [Jacob F. et al, 1963] that , with the aid of regulatory DNAsequences that are located on this replicon itself or on anotherreplicon present in the same microorganism, can be transported entirelyor partially into plant cells (example: the Ti-plasmid of Agrobacteriumtumefaciens).

T-DNA-border Sequences

DNA sequences that, in one or more copies, effect DNA transfer intoplant material with the aid of microbial functions.

Cargo-DNA

A DNA of homologous or heterologous origin or a combination ofhomologous and heterologous DNA or a DNA prepared fully or partially bysynthetic means, artificially inserted into a DNA vector.

Genomic DNA

DNA derived from the genome of an organism.

c-DNA

Copy of a mRNA produced by reverse transcriptase.

Synthetic DNA

A DNA sequence that codes for a specific product or products or for abiological function and that is produced, fully or partially, bysynthetic means.

Heterologous Gene(s) or DNA

A DNA sequence that codes for a specific product or products or for abiological function and that originates from a species different fromthat into which the said gene is to be inserted; the said DNA sequenceis also referred to as a foreign gene or foreign DNA.

Homologous Gene(s) or DNA

A DNA Sequence that codes for a specific product or products or for abiological function and that originates from the same species as thatinto which the said gene is to be inserted

Plant Cell Cultures

Cultures of plant units such as, for example, protoplasts, cell culturecells, cells in plant tissues, pollen, pollen tubes, ovules, embryosacs, zygotes and embryos in various stages of development.

Plants

Any photosynthetically active member of the Planta kingdom that ischaracterised by a membrane-encapsulated nucleus, genetic materialorganised in the form of chromosomes, membrane-encapsulatedcytoplasmatic organelles and the ability to carry out meiosis.

Plant Cell

Structural and physiological unit of the plant, consisting of aprotoplast and a cell wall.

Protoplast

"naked plant cell" without a cell wall isolated from plant cells ortissues, with the ability to regenerate to a cell clone or a wholeplant.

Plant Tissue

A group of plant cells that are organised in the form of a structuraland functional unit.

Plant Organ

A defined and clearly visible differentiated part of a plant such as,for example, a root, stem, leaf or embryo.

Fully Transformed Plants

Plants in which the genome of each cell has been transformed in thedesired manner.

Tandemly Duplicated Form

More than one viral DNA arranged in a head to head, a tail to tail or ahead to tail orientation, which would the infectious viral DNAsupposedly allow to become released based on an intramolecularrecombination via transcription, reverse transcription or other methodsof rearranging genetic material.

The present invention mainly relates to a method of introducing clonedviral DNA or functional equivalents thereof, that are normally notinfectious upon mechanical inoculation of plant material, into plantmaterial of plants that are naturally amenable, or, if not, areartificially made amenable, to transformation by a transfermicroorganism such as, for example, a transfer microorganism of thegenus Agrobacterium or viable parts thereof such as, for example, plantcell culture cells, which method comprises essentially the followingprocedural steps:

a) inserting cloned viral DNA or functional equivalents thereof, thatpreferably are capable of giving rise to a systemic infection, and whichoptionally may contain cargo DNA, into a T-replicon, for example aTi-plasmid or Ri-plasmid of an Agrobacterium, in the vicinity of one ormore T-DNA border sequences, the distance between said viral DNA and theT-DNA sequence or sequences being chosen such that viral DNA, includingany cargo DNA present, is transferred to plant material;

b) introducing the replicon into a transfer microorganism, for example amicroorganism of the genus Agrobacterium; and

c) infecting plant material with the transfer microorganism that hasbeen modified in accordance with b).

In a specific embodiment, the method according to the present inventionessentially comprises the following partial steps:

a) isolating viral DNA or functional equivalents thereof (as describedhereinafter), that preferably still have the potential for giving riseto a systemic infection upon incorporation into a plant or viable partsthereof, from infected plant material, and cloning said DNA in vectorsof a suitable bacterium such as, for example, Escherichia coli;

b) constructing a plasmid based on a T-replicon, for example aTi-plasmid or Ri-plasmid of an Agrobacterium, preferably containing morethan one viral genome or parts thereof that are in the vicinity of, butpreferably between, one or more T-DNA border sequences, the distancebetween the viral DNA and the T-DNA border sequence or sequences beingchosen such that said viral DNA, including any cargo DNA insertedthereinto, is transferred to plant material;

c) constructing a vector system by transferring the plasmid of step b)to a transfer microorganism (for example Agrobacterium tumefaciens orAgrobacterium rhizogenes);

c₁) optionally pretreating the so-transformed microorganism with plantexudate from dicotyledonous plants containing one or more compounds ofthe formula I, or with one or more compounds of the formula I in pureform;

d) growing the transfer microorganisms containing the T-replicon of stepb) in a suitable culture medium known per se;

e) infecting plant material, but especially the meristematic regions ofthe said plant material, with the vector system constructed inaccordance with c) and/or c₁), and thereby preferably releasing saidviral DNA giving rise to a systemic infection.

Within the scope of the present invention there are to be understood byviral DNA and its functional equivalents especially the following typesof DNA:

double stranded DNA forms of single-stranded DNA viruses (for exampleGemini viruses, such as Maize Streak Virus (MSV)) and functional partsthereof;

cDNA copies of viral RNA or viroid RNA (for example of Tobacco-Mosaicvirus or

Cadang-Cadang viroid) and functional parts thereof;

any viable mutants of viruses and functional parts thereof;

portions of viral DNA that are still capable of giving rise to asystemic infection;

equivalents of the above-listed types of DNA in tandem form and

equivalents of the above-listed types of DNA with incorporatedCargo-DNA.

It is possible to employ as the viral DNA that can be used within thescope of the process according to the invention, without this implyingany limitations, for example DNA of Caulimo viruses, includingCauliflower Mosaic Virus (CaMV). Representatives from the Caulimoviruses group, but especially Cauliflower Mosaic Viruses, are especiallysuitable for use within the scope of the process according to theinvention, since owing to their genome structure (double-stranded DNA)they are directly accessible to genetic manipulation.

Besides, also representatives of the Gemini viruses, the genome of whichis constructed from single-stranded (ss) DNA, can be suitably usedwithin the scope of the present invention as vectors for transferringgenetic material. This is, because the Gemini viruses form ds-DNA in thecourse of their development cycle and are thus accessible to directgenetic manipulation. To be mentioned here by way of exemplificationare, for example, Bean Golden Mosaic Virus (BGMV), Chloris StriateMosaic Virus (CSMV), Cassave Latent Virus (CLV), Curly Top Virus (CTV),Maize Streak Virus (MSV), Tomato Golden Mosaic Virus (TGMV) and WheatDwarf Virus (WDV).

Suitable transfer microorganisms that are capable of transferringgenetic material to plants and can be used in the process according tothe invention are especially microorganisms that contain a T-replicon.

There are to be understood by microorganisms that contain a T-repliconespecially bacteria, preferably soil bacteria and, of these, especiallythose of the genus Agrobacterium.

Obviously, only strains of bacteria that are harmless, that is to say,for example strains of bacteria that are not viable in a naturalenvironment or that do not cause any ecological problems, can be usedwithin the scope of the process according to the invention.

A suitable T-replicon is especially a bacterial replicon, such as areplicon of Agrobacterium, especially a Ti- or Ri-plasmid of anAgrobacterium.

Ti-plasmids have two regions that are essential for the production oftransformed cells. In dicotyledonous plants one of these, thetransfer-DNA region, is transferred to the plant and leads to theinduction of tumors. The other, the virulence-conferring (vir) region,is essential only for the development but not for the maintenance of thetumours. The transfer-DNA region can be increased in size byincorporating foreign DNA without its ability to be transferred beingimpaired. By removing the tumour-causing genes, as a result of which thetransgenic plant cells remain non-tumorous, and by incorporating aselective marker, the modified Ti-plasmid can be used as a vector forthe transfer of genetic material into a suitable plant cell.

The vir-region effects the transfer of the T-DNA region of Agrobacteriumto the genome of the plant cell irrespective of whether the T-DNA regionand the vir-region are present on the same vector or on differentvectors within the same Agrobacterium cell. A vir-region on a chromosomelikewise induces the transfer of the T-DNA from a vector into a plantcell.

Preferred is a system for transferring a T-DNA region from anAgrobacterium into plant cells which is characterised in that thevir-region and the T-DNA region lie on different vectors. Such a systemis known as a "binary vector system" and the vector containing the T-DNAis called a "binary vector".

Any T-DNA-containing vector that is transferable into plant cells andthat allows detection of transformed cells is suitable for use withinthe scope of this invention.

Preferred within the scope of the present invention is a T-replicon suchas, for example, a Ti-plasmid or an Ri-plasmid of an Agrobacterium thatcontains, adjacent to one or more T-DNA border sequences, but preferablybetween the said border sequences, cloned viral DNA, for example DNA ofCauliflower Mosaic Virus (CaMV) or Maize-Streak Virus (MSV), which, ifdesired, may contain incorporated Cargo-DNA, the distance between viralDNA and the T-DNA border sequence(s) being chosen such that the viralDNA, including any Cargo-DNA that may be present, is transferred intoplant material.

The viral DNA to be introduced into the plant cell is preferablyrepresented by one or more viral replicons or parts of a viral repliconincorporated in a manner that allows release and replication of theviral replicon in the plant cell independently of the chromosomal DNA.

Especially preferred are constructions that contain more than one viralDNA in a tandemly duplicated form in a head to head, a tail to tail or ahead to tail arrangement, which would the infectious viral DNA allow tobecome released based on an intramolecular recombination viatranscription, reverse transcription or other methods of rearranginggenetic material.

It is possible to use as Cargo-DNA either homologous or heterologousgene(s) or DNA as well as synthetic gene(s) or DNA in accordance withthe definition given within the scope of the present invention.

The coding DNA sequence can be constructed exclusively from genomic DNA,from cDNA or from synthetic DNA. Another possibility is the constructionof a hybrid DNA sequence consisting of both cDNA and genomic DNA and/orsynthetic DNA.

In that case the cDNA may originate from the same gene as the genomicDNA, or alternatively both the cDNA and the genomic DNA may originatefrom different genes. In any case, however, both the genomic DNA and/orthe cDNA may each be prepared individually from the same or fromdifferent genes.

If the DNA sequence contains portions of more than one gene, these genesmay originate from one and the same organism, from several organismsthat belong to more than one strain, one variety or one species of thesame genus, or from organisms that belong to more than one genus of thesame or of another taxonomic unit (kingdom).

The present invention relates also to the construction of cargo DNAcomprising chimaeric recombinant DNA molecules that comprise anexpressible DNA, but especially a structural gene, preferably aheterologous structural gene, in operable linkage with expressionsignals active in plant cells, such as promoter and terminationsequences, as well as, optionally, with further coding and/or non-codingsequences of the 5' and/or 3' region.

There are suitable for use in the process according to the inventionespecially all those structural genes which upon expression lead to aprotective effect in the transformed plant cells and also in the tissuesdeveloping therefrom and especially in the plants, for example increasedresistance to pathogens (for example to phytopathogenic fungi, bacteria,viruses, etc.); resistance to chemicals [for example to herbicides (e.g.triazines, sulfonylureas, imidazolinones, triazole pyrimidines,bialaphos, glyphosate, etc.), insecticides or other biocides];resistance to adverse environmental factors (for example to heat, cold,wind, adverse soil conditions, moisture, dryness, etc.).

Within the scope of this invention, special mention is to be made ofstructural genes that are associated with the control of plant pathogensand parasites.

Resistance to insects can be conferred, for example, by a gene codingfor a polypeptide that is toxic to insects and/or their larvae, forexample the crystalline protein of Bacillus thuringiensis [B.t.].Especially preferred within the scope the present invention aresynthetic B.t. genes.

A second class of proteins mediating resistance to insects comprises theprotease inhibitors. Protease inhibitors are a normal constituent ofplant storage structures and are therefore normally located in vacuolesor protein bodies. It has been demonstrated that a Bowman-Birk proteaseinhibitor isolated from soybeans and purified inhibits the intestinalprotease of Tenebrio larvae [Birk et al (1963)]. The gene that codes forthe trypsin inhibitor from the cowpea is described in Hilder et al(1987).

A gene that codes for a protease inhibitor can, in a suitable vector, bebrought under the control of a plant promoter, especially of aconstitutive promoter, for example the CaMV 35S promoter. The gene, forexample the coding sequence of the Bowman-Birk protease inhibitor fromthe soybean, can be obtained by the cDNA cloning method. A furtherpossible method of producing a protease inhibitor is syntheticmanufacture, provided that the protease inhibitor comprises fewer than100 amino acids, for example the trypsin inhibitor of the lima bean. Thecoding sequence can be predicted by reverse translation of the aminoacid sequence. In addition, there are incorporated at both endsrestriction cleavage sites suitable for the vector desired in eachparticular case. The synthetic gene is produced by synthesis ofoverlapping oligonucleotide fragments of from 30 to 60 base pairs, byfirst subjecting those fragments to a kinase reaction, then linking themto one another [Maniatis et al (1982)] and finally cloning them in asuitable vector. By means of DNA sequencing it is then possible toidentify a clone that has the insert in a correct orientation. Forinsertion into the protoplasts, isolated plasmid DNA can be used

In this connection, mention should also be made of hydrolytic enzymes,which are capable of bringing about the breakdown of the cell walls ofplant pathogens themselves, or at least assist that breakdown inconjunction with other substances in the sense of synergy.

The majority of insects, for example, have a cuticular skeleton in whichchitin micelles in lamellar layers are embedded in a base substance. Agreat many phytopathogenic fungi also contain chitin as an integral partof their hypha and spore structures, for example Basidiomycetes (smutand rust fungi), Ascomycetes and Fungi imperfecti (including Alternariaand Bipolaris, Exerophilum turcicum, Colletotricum, Gleocercospora andCercospora). Chitinase is capable of inhibiting the mycelial growth ofcertain pathogens in vitro. A plant organ or tissue that is capable ofexpressing chitinase constitutively or in response to the penetration ofa pathogen could therefore protect itself from attack by a large numberof different fungi.

A further gene, which encodes an enzyme which presumably plays a centralrole in the plant's defence mechanism against pathogens is theβ-1,3-glucanase gene, that may thus also be used for protecting plantsagainst a fungal attack, alone or im combination with a chitinase gene.

A further class of genes that may be used within the scope ot thisinvention are the so-called lytic peptides. These are natural orsynthetic peptides having anti-pathogenic activity which are capable ofpenetrating, lysing or otherwise damaging the cell membrane ofpathogens. Representatives of such lytic peptides that may be usedwithin the scope of the present invention are known both from animalsources [including insects] and from plant and microbial sources andinclude, for example, the defensines, cercopines, thionines andmellitines of mammals, and the defensines, magainines, attacines,dipterines, sapecines, caerulines and xenopsines of insects, and hybridsthereof. The amino acid sequences of various lytic peptides are shown inthe following publications: WO 89/11291; WO 86/04356; WO 88/05826; US4,810,777; WO 89/04371.

Lytic peptides in the broadest sense of the term are also to beunderstood as being compounds whose ability to penetrate, lyse or damagecell membranes is based on enzymatic activity, for example lysozymes andphospholipases.

Moreover, reciprocal use of expression and exogenous application mayalso be envisaged, the lytic peptides especially being suitable for thelatter purpose, in conjunction with the auxiliaries and/or additivescustomarily used for this purpose.

A further class of genes that may be used within the scope of thepresent invention comprises genes which encode pathogenesisrelatedproteins [PRPs] such as PR-1A, PR-1B, PR-1C, PR-R major, PR-R minor,PR-P, PR-Q, PR-2, PR-2', PR-2", PR-N, PR-O, PR-O', PR-4, SAR8.2a-e,cucumber chitinase/lysozyme, cucumber basic peroxidase, tobacco basicglucanase and tobacco basic chitinase/lysozyme, tobacco acidicchitinase/lysozyme. Examples of the above genes and proteins includingchimeric genetic constructs comprising the said genes are provided inEP-A 392,225 and in the co-pending U.S. patent application Ser. No.848,506.

The DNA sequence according to the invention can also be used in idealmanner for the production of desirable and useful compounds in the plantcell as such or as part of a unit of higher organisation, for example atissue, callus, organ, embryo or a whole plant.

Genes that may also be used within the scope of the present inventioninclude, for example, those which lead to increased formation of reserveor stored substances in leaves, seeds, tubers, roots, stems, etc. or inthe protein bodies of seeds. The desirable substances that can beproduced by transgenic plants include, for example, proteins,carbohydrates, amino acids, vitamins, alkaloids, flavins, perfumes,colourings, fats, etc.

There may also be associated with the DNA sequence according to theinvention structural genes that code for pharmaceutically acceptableactive substances, for example hormones, immunomodulators and otherphysiologically active substances.

The genes that can come into consideration within the scope of thisinvention therefore include, but are not limited to, for example,plant-specific genes, such as the zein gene from maize, the avenin genefrom oats, the glutelin gene from rice, etc., mammal-specific genes,such as the insulin gene, the somatostatin gene, the interleukin genes,the t-PA gene, etc., or genes of microbial origin, such as the NPT IIgene, etc. and synthetic genes, such as the insulin gene, etc.

Apart from naturally occurring structural genes that code for a usefuland desirable property, within the scope of this invention it is alsopossible to use genes that have been modified previously in a specificmanner using chemical or genetic engineering methods.

Furthermore, the broad concept of the present invention also includesgenes that are produced entirely by chemical synthesis. Genes or DNAsequences that may be used within the scope of the present invention aretherefore both homologous and heterologous gene(s) or DNA and alsosynthetic gene(s) or DNA according to the definition given within thescope of the present invention. The insulin gene may be mentioned atthis point as an example of a synthetic gene.

In order to ensure the expression of the said structural genes in theplant cell, it is advantageous for the coding gene sequences first to belinked in operable manner to expression sequences capable of functioningin plant cells.

The hybrid gene constructions within the scope of the present inventiontherefore comprise, in addition to the DNA sequence according to theinvention, one or more structural gene(s) and, in operable linkagetherewith, expression signals which include both promoter and terminatorsequences and other regulatory sequences of the 3' and 5' untranslatedregions.

Any promoter and any terminator capable of bringing about an inductionof the expression of a coding DNA sequence (structural gene) may be usedas a constituent of the hybrid gene sequence. Especially suitable areexpression signals originating from genes of plants or plant viruses.Examples of suitable promoters and terminators are those of theCauliflower Mosaic Virus genes (CaMV) or homologous DNA sequences thatstill have the characteristic properties of the mentioned expressionsignals. Also suitable are bacterial expression signals, especially theexpression signals of the nopaline synthase genes (nos) or the octopinesynthase genes (ocs) from the Ti-plasmids of Agrobacterium tumefaciens.

Within the scope of this invention, preference is given to the 35S and19S expression signals of the CaMV genome or their homologues which canbe isolated from the said genome using molecular biological methods, asdescribed, for example, in Maniatis et al (1982), and linked to thecoding DNA sequence.

Within the scope of this invention, homologues of the 35S and 19Sexpression signals are to be understood as being sequences that, despiteslight sequence differences, are substantially homologous to thestarting sequences and still fulfil the same function as those startingsequences.

In accordance with the invention there may be used as starting materialfor the 35S transcription control sequences, for example, the ScaIfragment of the CaMV strain "S", which includes the nucleotides6808-7632 of the gene map [Frank G et al (1980)]. The 19S promoter and5' untranslated region is located on a genome fragment between the PstIsite (position 5386) and the HindIII site (position 5850) of the CaMVgene map [Hohn et al (1982)]. The corresponding terminator and 3'untranslated region is located on an EcoRV/BgIII fragment betweenpositions 7342 and 7643 of the CaMV genome.

Also preferred within the scope of this invention are the expressionsignals of the CaMV strain CM 1841, the complete nucleotide sequence ofwhich is described in Gardner RC et al (1981).

A further effective representative of a plant promoter that may be usedis an over-producing plant promoter. Provided that this type of promoteris operably linked to the gene sequence that codes for a desired geneproduct, it should be capable of mediating the expression of the saidgene sequence.

Over-producing plant promoters that may be used within the scope of thepresent invention include the promoter of the small subunit (ss) ofribulose-1,5-biphosphate carboxylase from soybeans and also the promoterof the chlorophyll-a/b-binding protein. These two promoters are knownfor the fact that they are induced by light in eukaryotic plant cells[see, for example, Genetic Engineering of Plants, An AgriculturalPerspective, Cashmore A (1983)].

Further promoters useful in the present invention to express anassociated structural gene are promoters whose expression are known tovary in a tissue specific manner such as, for example, the promoter ofthe maize phosphoenol pyruvate carboxylase (PEPC; Hudspeth, R. L. andGrula, J. W., Plant Molecular Biology 12:579-589, 1989). Also to bementioned here by way of exemplification is a maize pith preferredpromoter, or a pollen specific promoter.

A developmentally regulated promoter can also be used. Of course, in thepresent invention, any promoter which is functional in the desired hostplant can be used to direct the expression of an associated gene.

It is often advantageous to incorporate a leader sequence between thepromoter sequence and the adjacent coding DNA sequence, the length ofthe leader sequence being so selected that the distance between thepromoter and the DNA sequence according to the invention is the optimumdistance for expression of the associated structural gene.

Further regulatory DNA sequences that may be used for the constructionof chimaeric genes include, for example, sequences that are capable ofregulating the transcription of an associated DNA sequence in planttissues in the sense of induction or repression.

There are, for example, certain plant genes that are known to be inducedby various internal and external factors, such as plant hormones, heatshock, chemicals, pathogens, oxygen deficiency, light, stress, etc.

As an example of gene regulation by a plant hormone, mention should herebe made of abscisic acid (ABS), which is known to induce the excess ofmRNAs which occurs during the late embryonal phase in cotton. A furtherexample is gibberellic acid (GA3) which induces malate synthasetranscripts in castor beans and isoenzymes of a-amylase in the aleuronelayers of barley.

The activity of glucanase and chitinase in bean leaves can be markedlyincreased by treatment with the stress hormone ethylene. In the case ofchitinase, this induction effect is controlled via the promoter of thechitinase gene, and it was possible to demonstrate this by reporter genetests using a promoter from the chitinase gene of beans (Phaseolusvugaris).

The regulation of heat-shock-sensitive protein genes of soybeans hasbeen studied in detail Treating the plants for several hours at atemperature of 40° C. results in the de novo synthesis of so-calledheat-shock proteins. A large number of those genes have since beenisolated, and their regulation has been analysed in detail Theexpression of those genes is controlled primarily at the transcriptionlevel. For example, if the promoter of the hps70 gene is fused with theneomycin phosphotransferase II (NPT II) gene, the chimaeric gene soformed can be induced by a heat shock [Spena et al, 1985].

Another class of genes that are inducible in plants comprises thelight-regulated genes, especially the nuclear-coded gene of the smallsubunit of ribulose-1,5-biphosphate carboxylase (RUBISCO). Morelli et al(1985) have shown that the 5'-flanking sequence of a RUBISCO gene fromthe pea is capable of transferring light-inducibility to a reportergene, provided the latter is lined in chimaeric form to that sequence.It has also been possible to extend this observation to otherlight-induced genes, for example the chlorophyll-a/b-binding protein.

The alcohol dehydrogenase genes (adh genes) of maize have been thesubject of intensive research. The adh1-s gene from maize was isolated,and it was shown that a part of the 5'-flanking DNA is capable ofinducing the expression of a chimaeric reporter gene (e.g.chloramphenicol acetyl transferase; CAT) when the temporarilytransformed tissue was subjected to anaerobic conditions [Howard et al(1987)].

A further group of regulatable DNA sequences comprises chemicallyregulatable sequences that are present, for example, in the PR(pathogenesis-related) protein genes of tobacco and are inducible bymeans of chemical regulators such as those described in EP-A 332,104.

The regulatable DNA sequences mentioned by way of example above may beof both natural and synthetic origin, or they may comprise a mixture ofnatural and synthetic DNA sequences.

It is often advantageous for the expressible DNA, but especially thestructural gene that is to be inserted, to comprise a sequence thatcodes for an N- or a C-terminal signal peptide capable of functioning inthe plant cell, or to be linked in the 5'- or 3'-terminal region to sucha sequence.

That N-terminal signal peptide is a transport signal that is found atthe N-terminal end of proteins transported via the endomembrane systemThis signal sequence ensures that the said proteins first pass into theendoplasmic reticulum where the signal peptide is split offproteolytically from the precursor protein as soon as it has fulfilledits function. By virtue of its specific function, this type of signalpeptide sequence has been conserved to a high degree during evolution inall living cells, irrespective of whether they are bacteria, yeasts,fungi, animals or plants.

At the C-terminal end of vacuolar proteins, on the other side, sequencesmay be found that are involved in directing the expression of theassociated coding part to the plant vacuole. Examples of these so-called`vacuolar targeting` sequences are provided, for example, in EP-A462,065.

Moreover, the DNA molecule may comprise further sections of sequencethat code for peptide fragments which as a whole contribute towardsimproving the competence for admission into the vacuole, for example thepropeptide fragment discovered by Matsuoka K and Nakamura K in theN-terminal extension of sporamine [Matsuoka K and Nakamura K (1991)].

The present invention therefore also includes chimaeric geneticconstructions that comprise in operable linkage with a structural geneor any other expressible DNA sequences, further regulatory sections ofDNA sequence permitting, for example, specifically controlled inductionor repression of gene expression.

The different sections of DNA sequence comprising a T-replicon and oneor more viral DNAs, which optionally may contain Cargo-DNA comprisingone of the chimeric constructs described hereinbefore, can be linked toone another to form a functional unit by methods known per se. Suitablemethods include, for example, the in vivo recombination of DNA sequencesthat have homologous sections and the in vitro linking of restrictionfragments.

In the above in vivo and/or in vitro processes for assembling thedifferent sections of the said functional unit, cloning vectors may beinvolved such as, for example plasmid or virus (bacteriophage) vectorshaving replication and control sequences originating from species thatare compatible with specific host cells.

The cloning vector generally carries an origin of replication,especially an origin of replication that is capable of functioning in E.coli, in Agrobacterium or in both, and, in addition, specific genes thatlead to phenotypic selection features in the transformed host cellespecially to resistance to antibiotics or to specific herbicides. Thetransformed vectors can be selected on the basis of those phenotypicmarkers after transformation in a host cell.

Especially suitable within the scope of the present invention areso-called shuttle vectors, which can stably replicate not only in onebut in at least two different host organisms such as, for example, in E.coli and in Agrobacterium tumefaciens, in the presence of a suitableselection marker.

Selectable phenotypic markers that may be used within the scope of thisinvention include, for example, resistance to ampicillin, tetracycline,hygromycin, kanamycin, methotrexate, G418 and neomycin, but this list,which is given by way of example, is not intended to limit the subjectof the invention.

Suitable host cells within the scope of this invention are prokaryotes,including bacterial hosts, for example A. tumefaciens, E. coli, S.typhimurium and Serratia marcescens, and also cyanobacteria. Eukaryotichosts, such as yeasts, mycelium-forming fungi and plant cells, may alsobe used within the scope of this invention.

The splicing of the hybrid gene construction according to the inventioninto a suitable cloning vector is carried out using standard methods,such as those described, for example, in Maniatis et al (1982).

As a rule, the vector and the DNA sequence to be spliced in are firstcleaved with suitable restriction enzymes. Suitable restriction enzymesare, for example, those that yield fragments having blunt ends, forexample SmaI, HpaI and EcoRV, or enzymes that form cohesive ends, forexample EcoRI, SacI and BamHI.

Both fragments having blunt ends and those having cohesive ends that arecomplementary to one another can be linked again using suitable DNAligases to form a continuous uniform DNA molecule.

Blunt ends can also be produced by treatment of DNA fragments that haveprojecting cohesive ends with the Klenow fragment of the E. coli DNApolymerase to fill up the gaps with the corresponding complementarynucleotides.

On the other hand, cohesive ends can also be produced by artificialmeans, for example by the addition of complementary homopolymeric tailsto the ends of a desired DNA sequence and of the cleaved vector moleculeusing a terminal deoxynucleotidyl transferase, or by the addition ofsynthetic oligonucleotide sequences (linkers) that carry a restrictioncleavage site, and subsequent cleavage with the appropriate enzyme.

The above assembling procedure may preferably result in a recombinantDNA molecule comprising a T-replicon such as, for example, a Ti-plasmidor an Ri-plasmid of an Agrobacterium that contains, adjacent to one ormore T-DNA border sequences, but preferably between the said bordersequences, one or more viral DNAs, for example DNA of Cauliflower MosaicVirus (CaMV) or Maize-Streak Virus (MSV), which, if desired, may containincorporated Cargo-DNA preferably comprising one of the chimericconstructs outlined hereinbefore, the distance between viral DNA and theT-DNA border sequence(s) being chosen such that the viral DNA, includingany Cargo-DNA that may be present, is transferred into plant material.

The recombinant DNA according to the invention can than be introducedinto a transfer microoganism, but preferable into a transfermicroprganism of the genus Agrobacterium, using one of the methods wellknown in the art. The transfer is preferably carried out by "triparentalmating", as described in detail in Rogers S. G. et al (1986) and in thefollwing examples.

The thus obtained transfer microorganisms are then grown in a culturemedium and under conditions known per se.

In a specific embodiment of the present invention, the transfermicroorganisms such as, for example, Agrobacterium tumefaciens, areadvantageously grown in one of the nutrient media normally used forculturing microorganisms at a temperature of from 15° C. to 40° C. overa period of from 30 to 60 hours (h) in a stirred liquid culture. Thepreferred growing temperature is from 24° C. to 29° C. There then followone or more sub-culturing steps, preferably in the same medium,advantageously in a dilution ration of 1:20, each of which lasts for aperiod of from 15 to 30 h, preferably from 18 to 20 h. In these cases,too, the culture temperature is from 15° C. to 40° C. preferably from24° C. to 29° C.

If thermophilic microorganisms are used, the growing temperature may bedistinctly higher than 40° C.

Obviously, it is also possible for other culturing measures suitable forgrowing the transfer microorganisms to be carried out within the scopeof this invention.

For example, it is also possible to use solid culture media, forexample, can be produced using agarose or alginate or any other suitablesolidifying agent.

The thus pretreated transfer microorganisms can then be used fortransforming plant material, whereby the recombinant DNA according tothe invention becomes transferred into the cells of the said plantmaterial.

DNA transfer to plants can be effected by one of the known systems, forexample by the binary vector system described by An, G. et al, 1985.This vector system can be improved by inserting e.g. sequences for ahomologous recombination of the DNA to be transferred to the plant.

Suitable plant material comprises both whole plants as well as parts ofplants. Parts of plants are for example also protoplasts, cell culturecells, cells in plant tissue, pollen, pollen tubes, egg-cells,embryo-sacs, zygotes or embryos in different stages of development aswell as whole plants.

Within the scope of the present invention, it has surprisingly beenpossible to show that the frequency of transformation of the inoculatedplants depends not only to a decisive degree on the application site onthe plant, but also very especially on the stage of development of theparticular plant being tested, as well as on other parameters.

An important part of the present invention therefore relates to a moresophisticated differentiation of the application site on the plant andthus to the specifically directed application of the transformingmicroorganism-containing inoculation solution at precisely defined siteson the plant, resulting in a significant increase in the frequency oftransformation of the inoculated plants. Furthermore, the frequency oftransformation can be even further increased by suitable selection ofthe time of application as regards the stage of development of therecipient plant.

These observations have led to the surprising finding that by applying acombination of suitable procedural measures, involving, for example, theuse of a suitable plant material and a suitable inoculation site for theDNA probe to be introduced, it is possible to achieve that high atransformation frequencies, that would be no longer necessary to furtherrely on disease symptoms in order to verify a positive transformationevent. This would mean, however, that the Agrobacterium transformationsystem can now be applied directly to graminaceous monocots without anyviral DNA being involved.

The present invention thus also relates especially to a novel processfor inserting genetic material into plants, but especially intomonocotyledenous plants, or viable parts thereof, which is characterisedin that transfer microorganisms that are capable of inserting the saidgenetic material into monocotyledenous plants or viable parts thereofand that contain the genetic material to be inserted in a transportableform, are inoculated in the form of a microorganism suspension into ameristematic tissue region of the plants or of a viable part thereof.

In particular, the present invention relates to an improved process fortransforming monocotyledonous plants using strains of Agrobacterium thatare capable of carrying out the said transformation, which process ischaracterised in that the time of inoculation as regards the stage ofdevelopment of the recipient plant, and the site of inoculation in theregion of the growth zones, are so coordinated that there is asignificant increase in the rates of transformation that can be achievedby comparison with known processes.

The target plants to be infected with an Agrobacterium transfermicroorganism according to the invention are preferable those plants orviable parts thereof, that are in a state of competence for anAgrobacterium infection. This state of competence may be found duringall developmental stages of the recipient plant extending over a priodthat commences with the development of the plant embryo and ends withthe flowering stage, and thus with the growth and development(differentiation) phase of the recipient plant.

Considering this aspect plants that have reached the stage ofdevelopment extending between seed germination and the 4-leaf stage haveproved to be especially suitable for the application of the processaccording to the invention.

Preferred are 1- to 3-day-old seedlings in which the distance betweenthe scutellar node and the apical coleoptile tip is from 1 to 2 cm.Plants that are at a stage of development that renders possible a clearidentification of the coleoptilar node are, however, especiallysuitable.

Especially preferred are seedlings which are germinated from immatureembryos. The tissue of immature embryo-germinated seedlings is soft,indicating a less rigid cell wall. This may physically orphysiologically favour Agrobacterium mediated T-DNA transfer. Mostpreferred are seedlings having developed the fith and sixth leafprimordia.

In a further embodiment of the present invention, the inoculation of themicroorganism-containing transforming inoculation solution is carriedout on the immature developing embryo after pollination andfertilisation of the ovules by the sperm nucleus, but preferably beforethe seed coat has developed Immature embryos are either inoculatedimmediately after isolation or are first germinated up to 3 days in thedark before being involved into the inoculation procedure.

When using very early, non-germinated, immature embryos thosemorphological stages are preferred that already show signs ofdifferentiation. Especially preferred are immature embryos that havedeveloped at least the first leaf initials as well as later stages.

To prepare the inoculation solution, the cells are preferablycentrifuged off and resuspended in a concentration, suitable forinfection, in a suitable inoculation medium, for example in 1/20th partvolume of an MSSP medium [Stachel et al, 1985]. The infection process iscommenced in accordance with the invention by bringing theafore-described transfer microorganism into contact with the plantmaterial, for example by incubation with protoplasts, by wounding wholeplants or portions of tissue or, especially, by injection of themicroorganism suspension directly into the plant.

The introduction of the transforming microorganism-containinginoculation solution into the plant can be carried out by a wide varietyof methods, for example by artificially wounding the epidermal tissueand rubbing the microorganism-containing transforming suspension intothe wounded tissue, by incubating [co-cultivating] the transfermicroorganism together with the wounded plant tissue or, alternatively,a plant protoplast, or by injecting the transforming suspension into theplant material to be transformed.

Injection of the inoculation solution using a hypodermic syringe ispreferred, by means of which a very accurately located and thusspecifically directed application at precisely defined sites on theplant can be effected.

As a rule, hypodermic syringes with exchangeable needles having across-section of from 0.1 to 0.5 mm are used, adapted to therequirements and special demands of the plant species concerned and toits stage of development at the time of application. The volume appliedalso varies as a function of the plant species concerned and its stageof development and ranges from 1 to 20 μl, an application volume of from5 to 10 μl being preferred.

Obviously, it is also possible to use other suitable aids for thetargeted application of the inoculation solution into the plant, suchas, for example, very fineyl drawn glass capillaries, by means of which,using micromanipulators, the smallest application quantities can beapplied into accurately defined tissue regions of the plant (such as,for example, the meristem). This approach would be especially suitableif immature plant embryos are involved owing to the limited size ofthese objects. In this case the preferred application volume is in arange of from 0.5 μl to 5 μl but especially from 2 μl to 4 μl.

The inoculation of the microorganism-containing transforming suspensionis carried out preferably in regions of the plant or viable partsthereof that contain meristematic tissue. These are portions of tissuethat are active as regards division and metabolism and that contain,especially, omnipotent embryonic cells from which are thus ultimatelyalso the starting point for the development of the germ cells.

A repeated application of the transforming microorganism containinginoculation solution into the meristematic tissue regions of the plantis especially preferred within the scope of this invention.

A particularly suitable application site for the insertion of thetransforming microorganism-containing suspension into plantlets alreadydifferentiated into stem, root and leaves in the boundary area betweenroot and stem, the so-called root collar.

In a special embodiment of the present invention, the application of thetransforming microorganism-containing suspension is effected on theseedling approximately from 1 to 3 days after germination. Preferredapplication sites are the coleoptile and coleorhiza areas.

Very good transformation results can be achieved by application in theimmediate vicinity of, or especially by application directly into, thecoleoptilar node.

Accordingly, a further especially preferred embodiment of the presentinvention is characterised in that the application of the transformingmicroorganism-containing inoculation solution is carried out from 1 to 3days after germination in the immediate vicinity of, or directly into,the coleoptilar node of the seedling.

In a further specific embodiment of the present invention, theapplication of the transforming microorganism-containing solution iscarried out directly into the coleoptilar node tissue after decapitatingthe tip of the coleoptile in the region of the coleoptilar node. Themajority of the plumule can be removed without the further developmentof the seedling being adversely affected.

A preferred method of application in this case, too, includes the use ofhypodermic syringes, it being possible for the depth of puncture to bevaried within specific limits as a function of the removal of thedecapitated region of the coleoptilar node. However, inoculationdirectly into the coleoptilar node tissue is in any case prefer.

Application of the inoculation solution can be effected either in theperipheral tissue areas or, especially, in the central part of theexposed coleoptilar node tissue, the areas of meristematic tissue beingespecially preferred.

If using immature embryos, apart from the inoculation techniques alreadymentioned it is also possible to use a process in which the embryo isfirst of all, in preparation, removed from the mother plant and thenbrought into contact with the transfer microorganism in a suitableculture medium [IK Vasil, 1984; Pareddy D. et al, 1987).

A further preferred method of application includes co-cultivating ofshoots of plant seedlings germinated from immature embryos, with theAgrobacterium containing solution, said shoots being obtainable bygerminating embryos on a suitable agar medium and isolating thedeveloping shoots from the seedlings by cutting just below thecoleoptilar node, where the shoot meristem is located. In particular,the shoots are dipped into the Agrobacterium suspension and thenpreferably subjected to vacuum infiltration. The infiltrated shoots arecultured on the agar plates of a suitable medium, but preferably a MSmedium.

The procedure for applying the inoculation solution to the plant orseedling may likewise vary, but can easily be optimised for differentspecies of plant. These optimising tests can be carried out, withoutappreciable expenditure by any person killed in the art within thelimits of a standard optimising programme in accordance with theguidelines of the present invention.

In addition to the parameters already mentioned, the concentration andthe growth phase of the inoculated transfer microorganisms are also ofsignificance as regards the efficiency of the transformation. Thepreferred concentration ranges from 10⁵ to 10¹⁰ organism per ml ofinoculation solution. An inoculation concentration of from 10⁷ to 10⁹organisms/ml is especially preferred.

Dilution experiments carried out within the scope of this invention haveshown that as dilution of the inoculation solution increases thefrequency of transformation decreases. The efficiency of theAgrobacterium-imparted DNA transfer to monocotyledonous plants is of thesame order as the DNA transfer to dicotyledonous host plants (Resultssection, Point D).

Possible variations within the scope of the process according to theinvention consequently reside in, for example, the choice of applicationmethod, the depth of puncture into the plant tissue, the composition andconcentration of the bacterial suspension, and the number ofinoculations carried out per infection.

A further measure that has proved to enhance the transformationfrequency is extra-wounding of the plant tissue to be inoculated. Thisis especially relevant in those case where the co-cultivation approachis used such as, for example, if shoots of plant seedlings germinatedfrom immature embryos are co-cultivated with an Agrobacterium-containingsolution.

The transfer of genetic material to monocotyledonous plants or to viableparts thereof in accordance with the invention can also be carried outafter pretreating the transfer microorganisms with a specific inducingagent consisting of an exudate of dicotyledonous plants or with certaincompounds that can be isolated from this plant exudate. Obviously, it isalso possible to use synthetically prepared or modified substances.

These inducing agents are especially compounds of the formula I ##STR1##in which R₁, R₂, R₃, R₄ and R₅, independently of one another, eachrepresents hydrogen or a substituent selected from the group comprisingOH, COOH, CHO, COCH₃, OCH₃ and CH═CHCOOH, with the proviso that aminimum of one and a maximum of three of the radicals R₁ to R₅ representhydrogen. These agents can be used individually or together.

Preferred within the scope of the invention are compounds of thefollowing formula Ia ##STR2## in which R₁ ' and R₄ ', independently ofone another, each represents H, OH or OCH₃ ;

R₂ ' represents H, COOH, CHO, COCH₃ or CH═CHCOOH; and

R₃ ' and R₅ ', independently of one another, each represents H or OH,with the proviso that a minimum of one and a maximum of three of theradicals R₁ ', R₂ ',

R₃ ', R₄ ' and R₅ ' represent hydrogen.

Examples of compounds of the formula I and Ia are, inter alia:

4-hydroxy-3,5-dimethoxyacetophenone,

4-hydroxy-3-methoxyacetophenone,

4-hydroxy-3,5-dimethoxybenzaldehyde,

4-hydroxy-3-methoxybenzaldehyde

4-hydroxy-3,5-dimethoxybenzoic acid,

3,4,5-trihydroxybenzoic acid,

3,4-dihydroxybenzoic acid,

2,4-dihydroxybenzoic acid,

β-hydroxybenzoic acid,

1,2,3-trihydroxybenzene and

1,2-dihydroxybenzene and

2-(3,5-dimethoxy-4-hydroxyphenyl)acrylic acid;

this list is not of a limiting nature.

The specifically mentioned representatives of compounds of the formula Iand la have been verified as natural constituents in plant exudates ofdicotyledonous plants and are known as inducers of the virulence(vir-)gene functions of the Agrobacterium tumefaciens Ti-plasmid.

In many cases it is advantageous if the inducer is added to the culturemedium from outside and thus sets the induction process in motion.

Plant cells or plants that have been transformed in accordance with thepresent invention can be selected by means of a suitable phenotypicmarker. Examples of such phenotypic markers, which are not, however, tobe construed as limiting, include antibiotic-resistance markers such as,for example, kanamycin-resistance genes and hygromycin-resistance genes,or herbicide-resistance markers such as, for example, the glyphosateresitance gene. Other phenotypic markers are known to the person skilledin the art and can likewise be used within the scope of this inventionsuch as, for example, the β-glucuronidase [GUS] gene.

Especially preferred within this invention is a GUS gene, that isembeded in a sequence of eukaryotic origin, which has been shown to havea enhancing influence on the post-transcriptional espression efficienyin plant cells.

By using the process according to the invention it is possible to obtainnot only transgenic plants with transformed somatic cells, but alsoespecially plants that contain transformed germ cells from which, in thecourse of further cell and tissue differentiation, transformed ovulesand/or pollen can develop.

After fertilisation with participation of transformed ovules and/ortransformed pollen, seeds are obtained that contain transgenic embryosand that can be used to produce. transgenic plants.

The method of this invention is suitable for infecting all plants withvirus. Of the systematic units Gymnospermae and Angiospermae (includingornamentals), the latter are preferred.

Among the Angiospermae, plants of particular interest are, in additionto deciduous trees and shrubs, plants of the following families:Solanaceae, Cruciferae, Malvaceae, Compositae, Liliaceae, Vitaceae,Chenopodiaceae, Rutaceae, Cucurbitaceae, Bromeliaceae, Rubiaceae,Theaceae, Musaceae or Gramineae and of the order Leguminosae, inparticular of the family Papilionaceae. Preferred plants arerepresentatives of the Solanaceae, Cruciferae and Gramineae families.

The high yield cultivated plants such as maize, rice, wheat, barley,rye, oats or millet are to be singled out for special mention.

Target crops are for example those of plants of the genera Solanum,Nicotiana, Gossypium (cotton), Brassica (rape), Beta, Pisum, Phaseolus,Glycine, Helianthus, Allium, Triticum (wheat), Hordeum (barley), Avena(oats), Setaria, Sorghum (millet), Oryza (rice), Zea (maize), Cydonia,Pyrus, Malus, Rubus, Fragaria, Prunes, Arachis, Secale, Panicum,Saccharum, Coffea, Camellia, Musa, Ananas, Vitis, Citrus and Persea(avocado).

Of particular commercial importance is the range of hosts of MaizeStreak Virus, which includes numerous monocotyledonous cultivated plantsand cereals such as, for example, maize, rice, wheat, millet, sorghumand various African grasses.

The process according to the invention is especially suitable forinfecting whole plants from the class of Monocotyledoneae or viableparts of those plants, such as, for example, plant tissue cultures orcell culture cells, with viral DNA and equivalents thereof. Thisinvention therefore also relates to the transformed protoplasts, plantcells, cell clones, cell aggregates, plants and seeds and progenythereof resulting from the process according to the invention, that havethe novel property resulting from the transformation, and also to allhybridisation and fusion products of the transformed plant material thathave the novel properties produced by the transformation.

The present invention also relates to transformed whole plants andviable parts of those plants, especially pollen, ovules, zygotes,embryos or any other reproductive material emerging from transformedgerm-line cells.

The present invention furthermore includes also completely transformedplants that have been regenerated from viable parts of transformedmonocotyledonous plants.

Monocotyledonous plants that are suitable for the use according to theinvention include, for example, species from the following families:Alliaceae, Amaryllidaceae, Asparagaceae, Bromeliaceae, Gramineae,Liliaceae, Musaceae, Orchidaceae or Palmae.

Especially preferred are representatives from the Gramineae family, suchas, for example, plants that are grown over a large area and producehigh yields. The following may be mentioned as examples: maize, rice,wheat, barley, rye, oats and millet.

Other target crops for the application of the process according to theinvention are, for example, plants of the following genera: Allium,Avena, Hordeum, Oryzae, Panicum, Saccharum, Secale, Setaria, Sorghum,Triticum, Zea, Musa, Cocos, Phoenix and Elaeis.

A further object of the present invention thus relates to transgenicplants, but preferably to transgenic monocotyledonous plants, morepreferably to transgenic monocotyledonous plants of the Gramineae familyand most preferably to transgenic maize plants obtainable by a processaccording to the invention including the transgenic progeny of thosetransgenic plants.

It is thus a further object of the present invention to providetransgenic monocotyledonous plants of the Gramineae family, butpreferably a transgenic maize plant, which are obtainable by a methodaccording to the invention and the progeny thereof including propagulesand seeds, comprising in an expressible form a chimaeric DNA constructcomprising an expressible DNA in operable linkage with expressionsignals active in plant cells of graminaceous monocots, such as promoterand termination sequences, as well as, optionally, further coding and/ornon-coding sequences of the 5' and/or 3' region.

Successful transformation by transferring T-DNA to the test plantconcerned can be verified in a manner knwon per se, for example in thelight of diesease symptoms [if viral DNA is involved in thetransformation process], and also be molecular biological investigationincluding, especially, the "Southern blot" analysis.

The extracted DNA is first of all treated with restriction enzymes, thensubjected to electrophoresis in 1% agarose gel, transferred to anitrocellulose membrane [Southern, (1975)] and hybridised (DNA-specificactivities of from 5×10⁸ to 10×10⁸ c.p.m./μl) with the DNA to bedetected, which has previously been subjected to a nick-translation[Rigby et al,]. The filters arc washed three times for one hour eachtime with an aqueous solution of 0.03M sodium citrate and 0.3M sodiumchloride at 65° C. The hybridised DNA is made visible by blackening anX-ray film for from 24 to 48 hours.

The use of the method of this invention employing the above describedvector system affords numerous advantages compared with the methodsemployed hitherto, viz.:

broadening the host range of an normally dicotyledon-specific transfermicroorganism such as, for example, Agrobacterium tumefaciens orAgrobacterium rhizogenes to monocotyledons;

inducing infectivity in viruses which it has so far not been possible tomake infectious by artificial means (for example maize streak virus),by-passing natural vectors such as insects;

the possibility of manipulating viral DNA in a bacterial system such asE. coli;

increasing the host range of viruses;

simplifying inoculation by avoiding DNA purification and verysubstantially reducing the amount of inoculum required for inoculation;

systemically infecting a whole plant by using viral DNA or equivalentsthereof,

under control of bacterially coded functions, the T-DNA, including theselected viral DNA, can become integrated into the host genome. Asregeneration of whole plants from single plant cells aftertransformation with bacteria is possible, viral DNA can be introducedinto the nuclear genome of every cell in a plant. Such integrated virusgenomes

can then be transmitted sexually to offspring;

can prevent infection by other viruses;

can be a possible source of further copies of virus containing selectedcargo DNA and which escape from the integrated copy via transcription,reverse transcription, homologous recombination or other methods ofmodifying genetic material.

In addition, superinfection of plants containing parts of viral genomesintegrated into the nuclear DNA may a) permit the development of betterviral vectors, as the expression of viral genes from nuclear DNA couldmake it possible to replace viral DNA with foreign DNA in thesuper-infecting virus; and b) contribute to a better understanding ofhost-parasite relationships and thus to substantially better protectionof plants.

By means of the method of this invention, cargo DNA inserted into thevirus genome can also be transported into plant material in which itproliferates. The proliferation in plants of the virus, and thus also ofthe foreign gene transported by it, is especially advantageous wheneverit is desired to propagate plants asexually or to protect them directand in the shortest possible time against harmful influences (forexample by inserting a gene into the plants to impart resistance).

The method of this invention is in particular admirably suitable forinsinuating selected genes into plant material, for example adultplants, in which they then proliferate.

The method of this invention can also be utilised in the field of plantprotection for "immunising" plants against virus attack by means of atransfer microorganism as described above by transforming plants with aweakened non-pathogenic or only slightly pathogenic virus, which has theresult of protecting the plants from undesired further virus infections.

A further approach that may be used in the immunization process isintroducing and expressing viral coat protein genes, which have provedto achieve a protective action, which protects the plant from infectionwith the corresponding virus. The expression of other virus genes suchas, for example, satellite RNA also can result in a protective actionagainst further viral infections.

It is thus a further object of the invention to provide a method ofimmunizing plants against an undesired virus attack, wherein a DNAexhibiting a protective action against further viral infections isintroduced into the said plant to be protected by a method according tothe invention.

The following Example, in which CaMV and MSV, respectively, are used asviruses, E. coli as cloning bacterium and Agrobacterium tumefaciens asvehicle bacterium, illustrates in more detail the construction and useof a suitable vector system. This Example can also be performed insimilar manner with Agrobacterium rhizogenes.

(A) NON-LIMITING EXAMPLES GENERAL RECOMBINANT DNA TECHNIQUES

Since many of the recombinant DNA techniques employed in this inventionare a matter of routine for the person skilled in the art, it is betterto give a short description of these generally used techniques hererather than to describe them every time they occur. Except where thereis a specific indication to the contrary, all these procedures aredescribed in the Maniatis et al (1982) reference.

A. Cleaving with Restriction Endonucleases

A reaction batch typically contains about 50 to 500 μg/ml of DNA in thebuffer solution recommended by the manufacturer, New England Biolabs,Beverly, Mass. 2 to 5 units of restriction endonucleases are added foreach μg of DNA and the reaction batch is incubated for from one to threehours at the temperature recommended by the manufacturer. The reactionis terminated by heating at 65° C. for 10 minutes or by extraction withphenol, followed by precipitation of the DNA with ethanol. Thistechnique is also described on pages 104 to 106 of the Maniatis et al(1982) reference.

B. Treatment of DNA with Polymerase in Order to Produce Blunt Ends

50 to 500 μg/ml of DNA fragments are added to a reaction batch in thebuffer recommended by the manufacturer, New England Biolabs. Thereaction batch contains all four deoxynucleotide triphosphates inconcentrations of 0.2 mM. The reaction takes place over a period of 30minutes at 15° C. and is then terminated by heating at 65° C. for 10minutes. For fragments obtained by cleaving with restrictionendonucleases that produce 5'-projecting ends, such as EcoRI and BamHI,the large fragment, or Klenow fragment, of DNA polymerase is used. Forfragments obtained by means of endonucleases that produce 3'-projectingends, such as PstI and SacI, the T4 DNA polymerase is used. The use ofthese two enzymes is described on pages 113 to 121 of the Maniatis et al(1982) reference.

C. Agarose Gel Electrophoresis and Purification of DNA Fragments fromGels

Agarose gel electrophoresis is carried out in a horizontal apparatus, asdescribed on pages 150 to 163 of the Maniatis et as reference. Thebuffer used is the tris-borate buffer described therein. The DNAfragments are stained using 0.5 μg/ml of ethidium bromide which iseither present in the gel or tank buffer during electrophoresis or isadded after electrophoresis. The DNA is made visible by illuminationwith long-wave ultraviolet light. If the fragments are to be separatedfrom the gel, an agarose is used that gels at low temperature and isobtainable from Sigma Chemical, St Louis, Mo. After the electrophoresis,the desired fragment is cut out, placed in a plastics test tube, heatedat 65° C. for about 15 minutes, extracted three times with phenol andprecipitated twice with ethanol. This procedure is slightly differentfrom that described by Maniatis et al (1982) on page 170.

As an alternative, the DNA can be isolated from the agarose with the aidof the Geneclean kit (Bio 101 Inc., La Jolla, Calif., USA).

D. Addition of Synthetic Linker Fragments to DNA Ends

If it is desired to add a new endonuclease cleavage site to the end of aDNA molecule, the molecule is optionally first treated withDNA-polymerase in order to produce blunt ends, as described in thesection above. About 0.1 to 1.0 μg of this fragment is added to about 10ng of phosphorylated linker DNA, obtained from New England Biolabs, in avolume of 20 to 30 μl with 2 μl of T4 DNA ligase from New EnglandBiolabs, and 1 mM ATP in the buffer recommended by the manufacturer.After incubation overnight at 15° C., the reaction is terminated byheating at 65° C. for 10 minutes.

The reaction batch is diluted to about 100 μl in a buffer appropriatefor the restriction endonuclease that cleaves the synthetic linkersequence. About 50 to 200 units of this endonuclease are added Themixture is incubated for 2 to 6 hours at the appropriate temperature,then the fragment is subjected to agarose gel electrophoresis andpurified as described above. The resulting fragment will then have endswith endings that were produced by cleaving with the restrictionendonuclease. These ends are usually cohesive, so that the resultingfragment can then readily be linked to other fragments having the samecohesive ends.

E. Removal of 5'-terminal Phosphates from DNA Fragments

During the plasmid cloning steps, treatment of the vector plasmid withphosphatase reduces the recircularisation of the vector (discussed onpage 13 of the Maniatis et al reference). After cleavage of the DNA withthe correct restriction endonuclease, one unit of calf intestinalalkaline phosphatase obtained from Boehringer-Mannheim, Mannheim, isadded. The DNA is incubated at 37° C. for one hour and then extractedtwice with phenol and precipitated with ethanol.

F. Linking of DNA Fragments

If fragments having complementary cohesive ends are to be linked to oneanother, about 100 ng of each fragment are incubated in a reactionmixture of 20 to 40 μl containing about 0.2 unit of T4 DNA ligase fromNew England Biolabs in the buffer recommended by the manufacturer.Incubation is carried out for 1 to 20 hours at 15° C. If DNA fragmentshaving blunt ends are to be linked, they are incubated as above exceptthat the amount of T4 DNA ligase is increased to 2 to 4 units.

G. Transformation of DNA into E. coli

E. coli strain HB101 is used for most of the experiments. DNA isintroduced into E. coli using the calcium chloride method, as describedby Maniatis et al (1982), pages 250 and 251.

H. Screening of E. coli for Plasmids

After transformation, the resulting colonies of E. coli are tested forthe presence of the desired plasmid by means of a rapid plasmidisolation process. Two customary processes are described on pages 366 to369 of the Maniatis et al (1982) reference.

I. Large-scale Isolation of Plasmid DNA

Presses for the isolation of plasmids from E. coli on a large scale aredescribed on pages 88 to 94 of the Maniatis et al (1982) reference.

J. Cloning in M13 Phage Vectors

In the following description it is to be understood that thedouble-stranded replicative form of the phage M13 derivatives is usedfor routine processes, such as cleaving with restriction endonuclease,linking etc.

Unless there is a specific indication to the contrary, enzymes can beobtained from Boehringer, Biolabs (BRL). They are used in accordancewith the manufacturer's instructions unless otherwise indicated.

K. Southern Blot Analysis

The extracted DNA is first treated with restriction enzymes, thensubjected to electrophoresis in a 0.8% to 1% agarose gel, transferred toa nitrocellulose membrane [Southern EM (1975)] and hybridised with theDNA to be detected which has previously been subjected tonick-translation (DNA-specific activities of 5×10⁸ to 10×10⁸ c.p.m/μg).The filters are washed three times for 1 hour each time with an aqueoussolution of 0.03M sodium citrate and 0.3M sodium chloride at 65° C. Thehybridised DNA is made visible by blackening an X-ray film over a periodof 24 to 48 hours.

(B) AGROINFECTION OF DICOTS Example 1

Preparation of the Bacterial Vector pCa305 which Contains 1.3 CaMVGenomes

In the plasmid pHC79 [Hohn, B. et al, 1980], the small area between theEcoRI restriction site and the ClaI restriction site is replaced withthe Eco-ClaI fragment, originating from the plasmid pMON30 [a precursorof pMON120; Fraley R. T. et al, !, 1983] and encoding aspectinomycin/streptomycin resistance. This is done by initially mixingplasmids pHC79 and pMON30 [0.2 μg-1.0 μg each] to a total volume of 18μl with water. Then 2.0 μl of a 10-fold concentrated tris-HCl buffer[100 mM NaCl; 50 mM tris-Cl (pH 7.5); 10 mM MgCl₂ ; 1 mM dithiothreitol]are added. After addition of 1-5 units of each of the correspondingrestriction enzymes [EcoRI and ClaI], the entire batch is thoroughlymixed and incubated for2 to 3 hours at a temperature of 37° C.

To terminate the digestion, a `stop` solution of the followingcomposition is added:

    ______________________________________                                               4M          urea                                                                           50% sucrose                                                 50 mM EDTA                                                                    0.1% bromophenol blue                                                         pH 7.0                                                                      ______________________________________                                    

The fragments resulting from the digestion are resolved according tosize by gel electrophoresis. The agarose gel electrophoresis isperformed in a horizontal apparatus as described on pages 150-163 of theManiatis et al reference. The buffer used is the tris-acetate bufferdescribed therein. The DNA fragments are coloured by 0.5 μg/ml ofethidium bromide, which is either present in the gel or tank bufferduring the electrophoresis or else is added after the electrophoresis.The DNA is visualised by irradiation with longwave ultraviolet light.

If it is desired to separate the fragments from the gel, then an agarosewhich gels at low temperature and is available from Sugman Chemical, StLouis, Mo., will preferably be used. After the electrophoresis, thedesired fragment is excised, placed in a small plastic tube, heated forabout 15 minutes to 65° C., extracted three times with phenol andprecipitated twice with ethanol. This method has been slightly modifiedin comparison with that described by Maniatis et al (1982) on page 170.

Alternatively, the DNA can be isolated from the agarose by means of theGeneclean Kits (Bio 101 Inc., La Jolla, Calif., USA).

The DNA fragments isolated in the above described manner [the largeEcoRI/ClaI fragment of plasmid pHC79 as well as the small EcoRI/ClaIfragment bearing spectinomycin/streptomycin] are incubated in aconcentration of about 100 ng in a reaction mixture of 20 to 40 μl withabout 0.2 units of T4 DNA ligase supplied by New England Biolabs in thebuffer recommended by the manufacture. The incubation is carried out for1 to 20 hours at 15° C. The plasmid resulting from this ligase reactionis designated pV118.

In the pV118 plasmid so obtained, the 2.5 kB range of plasmid pV118 bcbetween the SalI and BstEII restriction sites is replaced with the 3.3kB fragment which has been previously excised from CaMV "S" [Hohn, T. etal, 1982] at the SalI and BstEII restriction sites.

Plasmid pV118 is initially digested in the above described manner withSalI and BstEII. Care must be taken that the restriction enzyme BstEIIemployed here is preferably used in a buffer of median ionicconcentration [50 mM NaCl 10 mM tris-Cl (pH 7.5); 10 mM MgCl₂ ; 1 mMdithiothreitol]. The incubation temperature is 60° C. Simultaneous useof these two restriction enzymes is therefore not possible. Digestion isconveniently commenced with the enzyme which is incubated at lower ionicconcentration, i.e. in this case with BstEII.

After digestion and separation of the fragments by gel electrophoresis,the large fragment is isolated from the gel and joined in a subsequentligase reaction under the above stated conditions to the small 3.3 kBfragment after digestion with SalI/BstEII of the CaMV strain CaMV "S".In the plasmid pCa292 so obtained a complete CaMV CM-4184 genome[Howarth A. J. et al, 1981] is inserted into the single remaining Sailrestriction site. This can be done by digesting plasmid pCa292 as wellas the CaMV strain CM-4184 with SalI under the conditions indicatedabove and then joining them together in a ligase reaction.

The plasmid pCa305, which contains 1.3 genomes of CaMV in tandemarrangement, is obtained in this manner [see FIG. 1].

Example 2

Construction of Control Plasmid pEA1

To establish that the transfer of the infectious cloned virus DNA to therecipient plant has not been caused by lysis of the Agrobacterium cells,the plasmid pGV1106 [Leemans J. et al, 1982], which has a broad hostrange, is cut with the enzyme EcoRI in accordance with the aboveparticulars and introduced into the single SphI restriction site ofpCa305. The digestion of pCa305 with SphI is effected under the givenconditions for the EcoRI digestion. The plasmid pEA1 so obtained isinserted into Agrobacterium tumefaciens, where it replicatesindependently.

Key to FIGS. 1 and 2:

    ______________________________________                                        Ap.sup.R :     ampicillin resistence                                            Sp.sup.R /Sm.sup.R : spectinomycin/streptomycin resistance                    ori: origin of replication                                                    bom: origin of mobilisation                                                   BstEII, SphI, SalI, EcoRI: restriction sites                                  I-VII: open reading frame of CaMV                                             kB: kilobases                                                               ______________________________________                                    

Example 3

Introduction of Plasmids pCa305 and pEA1 into Agrobacterium tumefaciens

3.1: Transformation of pCa305 and pEA1 in E. coli GJ23

The transformation of plasmids pCa305 and pEA1 in E. coli GJ23 (pGJ28,R64drd11) [van Haute E. et al (1983)] is carried out by means of thecalcium chloride method.

100 ml of a complete medium (L-medium) are inoculated with an overnightculture of E. coli host cells. The bacteria are cultivated to an opticaldensity of 0.2 to 0.5 [≡5×10⁷ cells/ml] (the determination of theoptical density is made at a wavelength of 650 nm). The cells arethereafter sedimented for 5 to 10 minutes [at 3000-4000×g].

The bacteria pellet is resuspended in 1/10 volumes of MgCl₂ andsedimented once more. The sedimented bacteria are resuspended in 1/20volumes of CaCl2 and kept in an ice bath for 1.5 to 8 hours. Afterwards0.4 ml of the bacteria suspension is mixed with the plasmid DNA and themixture is kept for a further 30 minutes in an ice bath.

The bacteria can be additionally subjected afterwards to a brief heatshock [2 min at 42° C.] and, after addition of 5 ml of liquid fullmedium, cultivated further for 30 minutes at 37° C. The bacteria arethen sedimented once more and concentrated in 1 ml of liquid fullmedium. Afterwards 0.1 ml of this concentrate is streaked on L-agarwhich is enriched with 50 μg/ml ampicillin, 100 μg/ml streptomycin and50 μg/ml spectinomycin [in case of pCa305] and additionally 50 μg/mlkanamycin [in case of pEA1].

3.2: Conjugal Transfer

The E. coli strain GJ23 permits the conjugal transfer to Agrobacteriumtumefaciens of plasmids which have a born restriction site. Therecipients are two different Agrobacterium strains which both originatefrom A. tumefaciens stain A136 and thus contain the wild type Ti-plasmidpTiBo542 [Hood, E. E. et al (1984)].

Cultures of the donor and recipient strains are cultivated overnight and0.25 ml of each culture are mixed together. The bacteria are thenconcentrated on a 0.22 μm millipore filter which is placed on anLB-medium. The conjugation batch is incubated overnight at a temperatureof 28° C. The filter is then resuspended in a λ-buffer. Selection of theexconjugants is made by plating out suitable dilutions of thissuspension on selective medium.

3.3: Agrobacterium tumefaciens A136 (pTiBo542. pEAP18::pCa305)

(a) The strain A. tumefaciens A136 (pTiBo542, pEAP18) is used asrecipient for the plasmid pCa305 (pTiBo542, pEAP18). pEAP18 is a binaryvector which is constructed by starting from plasmid pGA472 [An G. et al(1985)]. Said plasmid is initially incubated with the restriction enzymeBamHI in a buffer of median ionic concentration [50 mM NaCl, 10 mMtris-Cl (pH 7.5); 10 mM MgCl₂ ; 1 mM dithiothreitol] at a temperature of37° C. in accordance with the above description, followed by digestionwith EcoRI at high salt concentration.

The EcoRI-BamHI fragment of plasmid pGA472 is replaced with the 2.6 kBEcoRI-BglII fragment of plasmid pHC79 [Hohn T. et al (1980)], whichcontains between the T-DNS border sequences a region for homologousrecombination with the plasmid pCa305. Care must be taken that thedigestion with BglII is carried out in a buffer of low ionicconcentration [10 mM tris-Cl (pH 7.5); 10 mM MgCl₂ ; 1 mMdithiothreitol], at a temperature of 37° C.

As plasmid pCa305 is unable to replicate in Agrobacterium tumefaciens,selection of the exconjugants on rifampicin, spectionmycin andstreptomycin affords the new stain Agrobacterium tumefaciens A136(pTiBo542, pEAP18::pCa305) in which the plasmid pCa305 has beenintegrated into the binary vector pEAP18 by homologous recombination[Leemans J. et al (1981)].

3.4: Agrobacterium tumefaciens A136 (pTiBo542. pEAP1)

(b) The strain Agrobacterium tumefaciens A136 (pTiBo542) is used asrecipient for plasmid pEA1. Absorption of the plasmid pEA1, which isable to replicate independently in Agrobacterium tumefaciens, leads tothe new stain Agrobacterium tumefaciens A136 (pTiBo542, pEAP1).Selection of the exconjugants is made on rifampicin (selective forAgrobacterium tumefaciens), kanamycin, spectinomycin and streptomycin.

The plasmids of the strains obtained as described in a) and b) above aretested by DNA isolation and restriction mapping.

(C) AGROINFECTION OF MONOCOTS

Maize Strains

For the inoculation experiments according to Examples 10, 13 and 16 theZea mays varieties `Golden Cross Bantam` (GB) and `B73` [Grimsley et al,1987] are used, respectively.

The inoculation experiments according to Examples 13 and 16 comprisingimmature maize embryos are accomplished with the inbred line A188 (Greenand Phillips, 1975), which can be obtained from T. Hein (FriedrichMiescher-Institut, Basel, Switzerland) and can be maintained for severalgenerations by selling in the greenhouse; further with Inbred bx/bx, amutant deficient in cyclic hydroxamates including DIMBOA (Coe et al,1988; Sahi et al., 1990), which can be obtained by P. King (FriedrichMiescher-Institut) or with Inbred W23 (b, r-g background), which can beobtained from V. Chandler (University of Oregon, Eugene [Chandler etal., 1989]). The McClintock line 880254A (sul, b, R-r background) can beobtained by B. Burr (Brookhaven National Laboratory, Upton, N.Y.).

Example 1

Construction of a Vector with Dimeric MSV Genome

MSV-genomes can be isolated from naturally occurring infected maizeplants in accordance with Mullineaux P. M. et al, 1984I, virion ss DNAacting as a matrix for the in vitro synthesis of double-stranded MSV-DNAusing klenow-polymerase I and an endogenous primer [Donson J et al.1984].

Another possibility consists of the isolation of double-stranded MSV-DNA("supercoiled MSV-DNA) directly from infected leaf material.Double-stranded MSV-DNA is formed as an intermediate during virusreplication. It is referred to as "replicative form DNA" or "RF-DNA".

The MSV-genomes are cloned by incorporating the RP-DNA or the in vitrosynthesised DNA into a pUC9 vector linearised by BamHI [Vieira T andMessing T, 1982]. The lax complementation test is used to identify therecombinant phages.

The next stage in the procedure is first of all to excise the clonedMSV-DNA at the single BamHI restriction incision site. The resultinglinearised DNA fragment is then isolate by gel-electrophoreticseparation of the DNA mixture [Maniatis et al. (1982)].

In virus strains having two or more BamHI restriction sites, either theNSV-Genome is partially digested or another suitable restriction site issought that appears only once in the MSV-genome. This applies also tothe case where there is no BamHI restriction site in the MSV-genome.

There then follows the splicing of the BamHI fragment in tendemarrangement into the BglII restriction site of the plasmid pGA471 [An Get al, 1985], which site is located between the T-DNA border sequences.This so-called tandem-cloning can be controlled by way of the respectiveconcentrations of vector and insert The insert should be present in theligation solution in excess. The preferred concentration ration is inthis case 10:1 (inser:vector).

The plasmit pGA471 is a so-called shuttle vector, which is stablyreplicated both in E. coli and in Agrobacterium tumefaciens in thepresence of tetracycline.

This vector possesses, in addition to the ColEl-replication origin lyingbetween the T-DNA border sequences, a further broad host rangereplication origin that makes it possible for the plasmit to be receivedin Agrobacterium tumefaciens. This replication origin originates fromthe plasmid pTJS75, a plasmid with a broad range of hosts and atetracycline-resistance gene, a derivative of RK2 [An G et al, 1985].

Other characteristic properties of the plasmid pGA471 are:

1) The possession between the T-DNA border sequences of variousrestriction sites that render possible incorporation of foreign DNA;

2) a cos-region of the bacteriophage λ, which permits cloning of largeDNA fragments (25-35 kb);

3) a chimar marker gene, composed of the control sequences of thenopalin synthase gene (nos) and a DNA sequence coding for neomycinphosphotransferase, and also

4) a bom-incision site, which renders possible transfer of the plasmidfrom E. coli into Agrobacterium tumefaciens.

The above-mentioned incubation solution containing the vector and theMSV-DNA to be spliced in, preferably in a concentration ration of 1:10,is used for the transformation of the E. coli strain DHl [Hanahan D. andMeselson M., 1980]. The selection is effected on the basis of thetetracycline resistance of the transformed clones and hybridisationexperiments using radioactively labelled MSV-DNA.

A selection of positive clones is then examined for the presence ofMSV-genomes in tandem arrangement For this purpose the plasmit DNA isisolated from the positive clones according to methods known per se[Maniatis et al, (1982)] and then subjected to restriction analysis.

One of the "tandem clones" is selected and is transferred from E. coliDHl to Agrobacterium tumefaciens (Rif^(R)) C58 (pTiC58).

The transfer is carried out by "triparental mating", as described indetail in Rogers S. G. et al (1986). In this case, rifampicin (100μg/ml) and tetracycline (5 μg/ml) are used for the selection. Thesuccessful transfer of the dimeric MSV-genome is tested by Southernhybridisation [Dhaese P. et al, 1979].

Agrobacterium tumefaciens (Rif^(R)) C58 (pTiC58) [Holsters et al, 1980]contains a wild-type Ti-plasmid with intact virulence functions,rendering possible the transfer of the shuttle vector into the plantcell.

The Agrobacterium strain transformed in the manner described above hasbeen given the following strain name: Agrobacterium tumefaciens(Rif^(R)) C58 (pTiC58; pEAP 200).

Example 2

Construction of a Control Vector

To construct a control vector without T-DNA border sequences, theplasmid pRK252 KanIII, a derivative of the plasmid pRK [Bevan M.,(1984)] is used, which contains no T-DNA border sequences.

The incorporation of the dimeric MSV-genome into the control vector iscarried out by splicing the above-described BamHI fragment in tandemarrangement, with the aid of a SalI/BamHI adaptor, into the SalIrestriction site of the plasmit pRK252 KanIII.

The transfer of the control vector into Agrobacterium tumefaciens l(Rif^(R)) C58 (pTiC58) is carried out by "triparental mating", asdescribed in detail in Rogers S. G. et al, (1986).

The transformed Agrobacterium strain has been given the following strainname: Agrobacterium tumefaciens (Rif^(R)) C58 (pTiC58; pEA 21).

Example 3

Construction of the Bacterial Vector pEAP 25

By exchanging a 0.65 kb Hind III-Sal I fragment in the cosmid pHC 79, aderivative of the E. coli plasmid pBR322 (Hohn and Collins, 1980), for a1.2 kb fragment from the transposon Tn 903 (Grindley et al, 1980), whichcarries a Kanamycin-resistance gene, the hybrid cosmid p22Gl is formed.The integration of the 1.2 kb fragment into the Hind III-Sal Irestriction site of pHC 79 is rendered possible by adding Hind E-Sal Ilinker sequences.

A 2.9 kb Sal I-Bst EII fragment that contains a gene coding forkanamycin-resistance in plants (Paszkowski et al, 1984) is excised fromthe plasmid pCaMV6Km and exchanged for a 2.4 kb Sal I-Bst EII fragmentfrom P22Gl.

The final construction of pEAP 25 is carried out by integration of theplasmid pB6 previously cut with Sal I into the Sal I incision site ofpEAP 1. Plasmid pB6 wad developed and made available by J. Davies of theJohn Innes Institute, Norwich, England. This plasmid has since beenpublished in N. Grimsley et al, 1987, under the name pMSV 12.

Plasmid pB6 contains a dimeric MSV-genome that has previously beencloned in the plasmid pACYC184 (Chang and Cohen, 1978).

Example 4

Construction of the Bacterial Vector pEAP 37

The bacterial vector pEAP 37 is constructed by inserting the plasmidpB6, which has previously been cut with Sal I, into the Sal Irestriction site of the plasmid pCIB 10. The plasmid pCIB 10 wasdeveloped and made available by Mary-Dell Chilton, CIBA-GIEGYBiotechnology Facility, Research Triangle Park, Raleigh N.C., U.S.A.

Example 5

Manufacture of the Bacterial Vector pEAP 40

A 1.6 mer of the MSV-genome [BglII-BamHI fragment (0.6mer.)+BamHI-BamHI-fragment, (monomer)] is spliced into the BamHIrestriction sites of the plasmic pTZ19R, which is described in Mead etal (1986). The resulting plasmid, called p3547, which contains a 1.6 merof the MSV-genome, is cut with EcoRI and then spliced into the EcoRIsite of the plasmid pCB200 (Rothstein et al, 1987). By means of thesesteps the MSV sequences are placed between the T-DNA border sequences ofpCIB200.

Example 6

Construction of the Bacterial Vector pMSV 109

5 μg of the plasmid pMSV12, the construction of which has already beendescribed in Example 3, are digested for a period of 2 hours at atemperature of 37° C. with BamHI in a buffer solution (Maniatis et al.,1982). The 2.7 kb DNA fragment resulting from this enzymatic digestionis, after electrophoretic separation of the sample in a 1% agarose-TAEgel (40 mM tris-HCl, 20 mM sodium acetate, 2 mM EDTA), eluted from thelatter and spliced into the single BamHI restriction site of the binaryT-DNA vector pBin19 (Bevan, 1984).

For the ligation, a 100-fold molar excess of the 2.7 kb MSV fragment (ofthe "insert") in relation to the vector pBin19, and a high T₄ -DNAligase concentration, are used in order to ensure a high rate ofincorporation of the dimeric MSV-DNA into the vector. in detail, theconcentrations used are 625 ng of pMSV DNA and 25 ng of pBin19 DNA,which are ligated at a temperature of 10° C. for a period of 16 hours inthe presence of 5 units of T₄ -DNA ligase in a total volume of 10 μl.Half of this ligation mixture is transformed into competend E. coli JM83rec^(A) cells, and plated out onto "Luria Broth" (LB)-agar (Maniatis etal, 1982) supplemented with 50 μg/ml of kanamycin sulphate and 40 μg/mlof 5-dibromo-4-chloro-3-indolylgalactoside (X-gal), and incubatedovernight at 37° C.

White colonies that contain the MSV-insert are selected and a clone thatcontains the dimeric MSV-insert in tandem arrangement (pMSV109) isselected for the conjugation into Agrobacterium tumefaciens C58Nal^(R)(Hepburn et al, 1985), which is carried out in accordance with a processdescribed by Ditta et al, 1980. The selection of exconjugants is carriedout on LB-agar containing 50 μg/ml of kanamycin sulphate and 50 μg/ml ofnalidixic acid. The selected colony, which in the inoculationexperiments described hereinafter initiates an infection in maize, iscatalogued as pMSV 114.

Example 7

Construction of a Control Vector (pEA 2) without T-DNA Border Sequences

To construct the control vector pEA 2, the Sal I restriction site of theplasmid pRK 252/kmIII, of a precursor-plasmid of pBIN19 (Bevan, 1984),is linked with the Sal I cut plasmid pB6.

The selection of pEA 2 is carried out on the basis of the kanamycin(KM^(R))- and chloramphenicol (Cm^(R))-resistance of the control vector.

Example 8

Introduction of the Plasmids pEAP 25. pEAP 37 and pEA 2 intoAgrobacterium tumefaciens

The plasmid pEAP 25 is cloned in bacteria of the strain Escherichia coliGJ23 (pGJ28, R64rd11) (van Haute el al, 1983). This E. coli strainrenders possible the transfer by conjugation of plasmids that have aborn incision site into Agrobacterium tumefaciens. The plasmids pEA 1,pEAP 37 and pEAP 40 are transferred via "triparental mating" intoAgrobacterium tumefaciens (Rogers, S. G. et al, 1986). The recipientstrains used are two Agrobacterium tumefaciens strains:

1) C58 (pTiC58) for the binary vectors pEAP 40, pEA 2 and pEAP 37

2) C58 (pTiC58), pEAP 18) for the plasmid pEAP 25.

Wild-type strains of Agrobacterium tumefaciens can be obtained from the"Culture Collection of the Laboratory of Microbiology, MicrobiologyDepartment of the University of Gent".

pEAP 25

The Agrobacterium strain C58 (pTiC58, pEAP 18) acts as a recipientstrain for the plasmid pEAP 25. pEAP 18 is a binary vector that isconstructed by replacing the 6.7 kb EcoRI-BamHI fragment of the plasmidpGA472 (An, G. et al, 1985) by the 2.6 kb EcoRi-BglII fragment of theplasmid pHC79 (Hohn, B. et al, 1980) which contains, between T-DNAborder sequences, a region for homologous recombination in the plasmidpEAP 25. Since the plasmit pEAP 25 does not replicate in Agrobacteriumtumefaciens, the selection of the exconjugants on rifampicin, kanamycinand carbenicillin yields the new Agrobacterium strain Agrobacteriumtumefaciens C58 (pTiC58, pEAP 29) in which the plasmid pEAP 25 has beenintegrated into the binary vector pEAP 18 by homologous recombination.

pEAP 37. pEAP 40

The mobilisation of the plasmide pEAP37 and pEAP40 from E. coli intoAgrobacterium tumefaciens via "triparental mating" results in theconstruction of a binary vector system.

pEA 2

The control plasmid pEA 2 is inserted into the Agrobacterium strain C58(pTiC58) where it establishes itself in the Trans-position to the Tiplasmid already present there.

The plasmids newly constructed in the manner described above are testedby way of DNA isolation and restriction mapping.

Example 9

Culturing the Agrobacterium strains (Rif^(R)) C58 (pTiC58: PEAP 200),(Rif^(R)) C58 (pTiC58, pEA21), C58(pTiC58, pEA 2) and C58 (pTiC58, pEAP37), C58 (pTiC58, pEAP29); C58 (pTiC58, pEAP 40) and also C58 (pTiC58,pMSV109 and the Manufacture of the Inoculation Solution

Before inoculation, the Agrobacterium strains are plated out onto YEBmedium [Bacto beef extract 5 g/l, Bacto yeast extract 1 g/l, peptone 5g/l, sucrose 5 g/l MgSO₄ 2 MM, pH 7.2), which has been augmentedbeforehand with 100 μg/ml of rifampicin and 25 μg/ml of kanamycin or 50μg/ml of nalidixic acid and solidified with 1.5% agar. After a culturingperiod of 48 h at a temperature of 28° C., a single colony is used toinoculate a liquid culture. The inoculation is carried out in 100 mlErlenmeyer flasks in a liquid YEB medium that has been augmented withantibiotics in the afore-mentioned concentration. Culturing is carriedout at a temperature of 28° C. on a stirring machine at a speed of 200r.p.m. The culturing period is 24 h.

Then, a second sub-culturing process is carried out in liquid medium ata dilution ratio of 1:20 under otherwise identical conditions. Theincubation period is in this case 20 h.

These steps lead to a population density of living agrobacteria ofapproximately 10⁹ /ml.

The bacteria cells are harvested by centrifuging and are thenresuspended in an equivalend volume of a 10 mM MgSO₄ solution that doesnot contain any antibiotics.

This suspension is referred to as an undiluted strain solution in thefollowing procedure. When preparing a series of dilutions, 10 mM MgSO₄solution is again used as diluent.

Example 10

Sterilisation and Germination of Maize Seeds

For the inoculation experiments plants of the varieties Golden CrossBantam, B 73, North Star and/or Black Mexican Sweetcorn are used all ofwhich can be successfully agroinfected.

For the following experiments, as a rule 3-day-old, previouslysterilised seedlings are used. The sterilisation of the seedlingscomprises the following process steps:

1. Sterilisation of the seeds in a 0.7% w/v calcium hypochloritesolution (250 ml solution/100 seeds). The seeds and solution arethoroughly mixed using a magnetic stirrer. After 20 minutes thesterilisation solution is decanted.

2. The seeds treated in this manner are then washed 3 times withdistilled water (250 ml dist. water/100 seeds) for 30 minutes each time.

The seeds sterilised in this manner are then introduced into seedchambers that have also already been sterilised. The seed chambers arepetri dishes which each contain 3 sterile Macherey-Nagel® round filtershaving a diameter of 8.5 cm and also approximately 10 ml of sterilewater.

20 seeds are introduced into each of these seed chambers and incubatedin the dark for approximately 3 days at a temperature of 28° C.

For the subsequent inoculation experiments, only seedlings in which thedistance between scutellar node and the apical coleoptile tip is 1-2 cmare used, in any case, however, it must be ensured that the coleoptilenode is clearly identifiable.

Example 11

Immature Embryo Production, Isolation, and Cultivation

The maize seeds used are obtained from the lines listed in Table 7. Allseeds are surface sterilized in 1,4% sodium hypochlorite for 20 min andwashed three times in sterile water. Aseptic seeds are germinated on wetfilter paper in Petri dishes at 28° C. for 3 days in the dark. Seedlingsare propagated subsequently in small pots in a plant growth chamberunder 16-hr light, 25° C., and 8-hr dark, 20° C., 20,000 lux lightregime with 50% humidity. After 2 to 3 weeks, well-grown seedlings aretransferred into 20-liter pots containing slow-release fertilizer andpropagated under the same light/dark regime. Alternatively, seedlingsare transferred into a greenhouse field and propagated under similarlight conditions. After 2 to 2.5 months, emerging ears are bagged andthe husks cut back as soon as the first silks appeared. One day later,newly emerging silks are pollinated with fresh pollen of either the same(selfed) or another plant of the same genotype (sibbed). Pollinated earsare protect with "Lawson" bags obtained from Funk Seeds (Bloomington,Ill.). Immature ears are harvested at the desired DAP, and immaturekernels are removed, surface sterilized for 20 min in 1.4% sodiumhypochlorite, and washed three times in sterile water.

Immature embryos are excised aseptically in a laminar flow bench usingsterilized forceps and scalpels. Embryos smaller than 1 mm in length areremoved with the help of a stereomicroscope. Excised embryos are placedwith the scutellar side down onto 1% agar solidified MS medium(Murashige and Skoog, 1962) containing 3% sucrose and 1 mg/literthiamine-HCl. Per plate, 30 to 50 immature embryos are either inoculatedimmediately after isolation or germinated up to 3 days in the dark at25° C. for 16 hr, followed by 8 hr at 20° C.

Immature embryos derived from one cob are always distributed onto fourMS plates. One plate is inoculated immediately after embryo isolation,the others are inoculated 1, 2, and 3 days after germination,respectively. Excised mature embryos from sterilized seeds for controlinoculations are treated in the same way.

Example 12

Inoculation of the Maize Seedlings

Hamilton hypodermic syringes (A 50 μl or 100 μl) fitted withexchangeable needles 0.4 mm in diameter are used to introduce theinoculation solution described under point 3. into the maize seedlings.

The inoculation solution is taken up into the hypodermic syringe in sucha manner that no air bubblers are formed.

12.1 Inoculation of 10-day-old Maize Plants

The inoculation of the bacteria-containing suspension into 10-day-oldmaize plants is carried out by various methods and at different sites onthe plant.

1. Application of 20 μl of bacterial suspension to one of the upperleaves and rubbing the suspension into the leaf with the aid ofcarborundum powder until the entire leaf appears wet (position A indiagram 1).

2. Injection of 10 μl of the bacterial suspension using a 100 μlHamilton hypodermic syringe into the central part of the plant.

a) exactly above the liguia of the primary leaf (position B in diagram1)

b) 1 cm below the ligula of the primary leaf (position C in diagram 1)

c) at the base of the plant in the so-called root collar, a meristematictissue from which adventitious roots later develop (position D indiagram 1).

12.2 Inoculation of 3-day-old Maize Seedlings

The inoculation of the bacterial suspension into 3day-old maizeseedlings is carried out by injection into the seedling using a 100 μlHamilton hypodermic syringe.

1. Injection of the bacterial suspension into the coleoptilar node byintroducing the hypodermic needle through the coleoptile, staring fromthe apical coleoptile tip and passing into the region of the coleoptilarnode (position E in diagram 2).

2. Injection of the bacterial suspension directly into the coleoptile, 2mm below the apical coleoptile tip (position F in diagram 2).

3. Injection of the bacterial suspension directly into the coleoptile, 2mm above the coleoptile node (position G in diagram 2).

4. Injection of the bacterial suspension directly into the coleoptilarnode (position H in diagram 2)

5. Injection of the bacterial suspension directly into the coleoptile, 2mm below the coleoptilar node (position I in diagram 2).

6. Injection of the bacterial suspension directly into the scutellarnode (position J in diagram 2).

7. Injection of the bacterial suspension into the scutellamode (byintroducing the hypodermic needle through the primary root, startingfrom the root tip and passing into the region of the scutellar node(position K in diagram 2).

12.3 Decapitation of the Coleodtile in the Region of the ColeoptilarNode

3-day-old maize seedlings are decapitated at various points in theregion of the coleoptilar node (see diagram 3).

1. 1 mm above the coleoptilar node

2. 2 mm above the coleoptilar node

3. 5 mm above the coleoptilar node.

The decapitated seedlings are then planted in moist earth and cultivatedin accordance with the conditions given under point 6.

The actual inoculation experiments with Agrobacterium are carried out onseedlings in which the coleoptile tips have, in preparation, beenremoved 2 mm above the coleoptilar node.

12.4 Cultivating the Treated Maize Plants and Maize Seedlings

Directly after the inoculation treatment the maize seedlings are plantedin moist earth and cultivated in the same manner as the 10day-old maizeplants at a temperature of 22° C. ±2° C. with permanent lighting withwhite (Phillips 400 W/G92/2) at 3000-5000 lux.

The plants are then examined daily for the presence of symptoms of avirus infection, which is characterised by the appearance of yellow dotsand/or streaks at the base of newly formed leaves.

Example 13

Inoculation of Immature Embryos

The apical meristem or the shoot apex of immature embryos as small as 1mm is punctured with a Microlance 26G³ /8 0.45×10 fine needle, and thesmaller embryos are punctured with a drawn out glass microcapillary.Immediately after puncturing, 2 to 4 μl of an overnight Agrobacteriumculture containing the MSV construct according to Example 5 is applied.Bacteria are obtained with a liter of 10⁹ cells per milliliter, washed,and resuspended in 10 mM MgSO₄ to the same concentration. Successivesubcultivations are done up to 3 days for each germination series. Afterevery subcultivation step, the presence of correct pLE1 sequences istested by restriction analysis after plasmid isolation by an alkalinelysis procedure (Sambrook et al., 1989). Inoculated immature embryos areincubated with the apical side on the MS medium for 24 hr in the dark,then flipped over and incubated for another day on the same medium under16hr light, 10,000 lux, 25° C. followed by an 8-hr dark, 20° C. regime.Embryos are then transferred onto 0.8% agar solidified MS mediumcontaining 3% sucrose, 1 mg/liter thiamine-HCl, 500 μg/ml cefotaxim(Hoechst, Frankfurt Germany), and 500 μg/ml carbenicillin againstAgrobacterium growth. After 1 week, immature plantlets are transferredinto Magenta boxes containing MS medium solidified with 0.8% agar andcontaining 2% sucrose and 1 mg/liter thiamine-HCl. Twelve DAP immatureembryos from the line B73 (Funk seeds) are inocuolated withAgrobacterium preinduced with acetosyringone.

Example 14

Scoring for MSV Symptoms

14.1: DNA Extraction from Infected Symptomatic Maize Plants

Approximately 400 mg (fresh weight) of young leaf tissue is first of allhomogenised in a mortar on ice, with the addition of 0.5 ml-1, 0 ml STEN(15% sucrose, 50 mM tris-HCl, 50 mM Na₃ EDTA, 0.25 M NaCl, pH 8) andsand (˜50 mg) to assist the tissue digestion. The homogenisate is thentransferred into a small centrifugation tube (1.5 ml) and centrifugedfor 5 minutes at a temperature of 4° C. in a table centrifuge at maximumspeed. The supernatant is discarded and the pellet is resuspended in 0.5ml of ice-cold SET (15% sucrose, 50 mM Na₃ EDTA, 50 mM tris-HCl, pH 8)while stirring first of all with a sterile toothed rod, and then brieflyusing a vortex mixer (5 seconds). Subsequently, 10 μl of a 20% SDSsolution and 100 μl of proteinase K (20 mg(ml) are added and mixed inand the whole is then heated in the small tube for 10 minutes at 68° C.After the addition of 3M sodium acetate (1/10 volume) the lysate isextracted twice with phenol/chloroform (3:1). The DNA is thenprecipitated by the addition of 2 parts by volume of ethanol and storedovernight at -20° C. Centrifugation (10 min.) in a table centrifuge atmaximum speed yields a DNA-containing pellet which is subsequentlydissolved in 40 , μl of TE buffer (40 mM tris-HCl, 1 mM Na₃ EDTA, pH 8).

Aliquots of this DNA solution are used for the "Southern blot"experiments (Southern EM, 1975).

14.2: Vir Gene Induction Assays

Immature shoots were scored 2 to 4 weeks after inoculation for MSVsymptom formation. With the exception of the mutant bx/bx, between 45and 95% of the inoculated immature embryos, depending on age andgenotype, survived the inoculation procedure. Within a germinationseries, ungerminated immature embryos had higher survival rates thangerminated embryos. Control inoculations with 10 mM MgSO₄ gave similarsurvival results. Therefore, the frequency of symptom formation wascalculated as the fraction of shoots with MSV symptoms per totalsurviving shoots.

Induction of an Agrobacterium vir gene by immature embryos was measuredqualitatively, as described by Grimsley et al (1989). An Agrobacteriumstrain with a lacZ insertion in the pinF ("plant inducible") locus ofthe Ti-plasmid virulence region was grown in YEB medium supplementedwith 100 μl/ml carbenicillin overnight at 28° C., subcultured into 1XM9medium (Miler, 1972) supplemented with 100 μg/ml carbenicillin overnightat 28° C., then diluted to OD₆₀₀ =0.1 in 1XM9 medium. One microliter 2%5-bromo-4 chloro-3-indole-galactose (X-Gal; Sigma) in dimethyl-formamidewas added to 500 μl of bacterium suspension, and cocultivation withwounded immature embryos was done overnight at 28° C. with 100 μl in amicrotiter dish. Acetosyringone (Sigma) in a final concentration of 100μM, added to the bacterium suspension, was used as a positive control.Blue spots on immature embryos and blue medium were scored as inducingthe pinF gene.

14.3: Histological Analysis of Immature Embryos

Embedding, thin sectioning, and staining with hematoxylin orsafranin/fast-green was done using standard procedures (Grimsely et al,1988).

Example 15

"Southern blot" Analysis

The extracted DNA is first of all treated with restriction enzymes andthen subjected to electrophoresis in 1% agarose gel, transferred onto anitrocellulose membrane [Southern, (1975)] and hybridised (DNA-specificactivities of 5×10⁸ to 10×10⁸ c.p.m./μg) with the DNA to be detected,which was previously been subjected to a nicktranslation [Rigby et al,]. The filters are washed three times for an hour each time with anaqueous solution of 0.03 M sodium citrate and 0.3 M sodium chloride at65° C. The hybridised DNA is made visible by blackening an X-ray filmfor from 24 to 48 hours.

Example 16

T-DNA Transfer to Maize Cells

16.1: Plasmid Constructions, Bacterial Strains and Culture Conditions,

The GUS gene used here has first been described by Schultze et al(1990). The plasmid pGUS23, containing this GUS gene in the pUC7 vector,has also been described previously in Puchta and Hohn (1991). PlasmidpBG5 is constructed by cloning the GUS gene-containing EcoRI fragment ofpGUS23 into the EcoRI site of the binary vector pBIN19 [Bevan (1984);see also Example 6]. The HindIII fragment containing the same GUS geneof pGUS23 is also cloned into the HindIII site of the binary vectorpCGN1589, described in McBride and Summerfelt (1990), resulting inplasmid pCG5. Plasmids are maintained in E. coli stain DH5α and isolatedas described hereinbefore. Plasmdis pBG5 and pCG5 are introduced intodifferent A. tumefaciens strains using the triparental-mating method ofRogers et al (1988). Table 1 lists Agrobacterium strains used.

The Agrobacterium strain C58C1 is described in Holsters et al (1980).

The Agrobacterium strain LBA4301 [pJK270] is described in Klapwijk et al(1979) and in Rogowsky et al (1987).

The Agrobacterium strains LBA4301 [pJK190, pCG5] and LBA4301 [pJK210,pCG5] [Rogowsky et al (1987)] are two different virB mutants, that aredeficient in an essential step in T-DNA transfer, and are used,therefore, as controls.

The Agrobacterium strains are grown in shaking liquid cultures at 28° C.for 48h in YEB medium [as to its' composition see Example 9]supplemented with appropriate antibiotics. They are subcultured in thesame medium following a 1:20 dilution, and grown for a further 20 h,reaching a final titre of 1-2×10⁹ cells/ml. Cells are then harvested bycentrifugation, washed with 10 mM MgSO₄ and resuspended in 10 MrM MgSO₄or in MS medium [Murashige & Skoog (1962)] to a final titre of 1-2×10¹⁰cells/ml.

16.2: Preparation of Maize Shoots

Maize lines Golden Cross Bantam (GB) and A188 are previously described[see Part B, Maize lines]. Line K55 was provided by Dr. V. Walbot(Department of Biological Sciences, Stanford University). GB seeds andimmature kernels of A188 and K55 harvested 14-17 days after pollinationare surface sterilized in 1.4% sodium hypochlorite and 0.05% SDS for 20min and washed 3 times for 5 min each in sterile water. Seeds aregerminated on water-wet filter paper at 28° C., in the dark. Embryos areisolated from immature kernels and germinated on agar MS medium in aphytotron under a regime of 16 h light (20 000 lux) and 8 h dark, at 25°C. Shoots are isolated from seedlings by cutting just below (about 1-3mm) the coleoptilar node where the shoot meristem is located

16.3 Cocultivation of Maize Shoots with Agrobacterium

Acetosyringone (AS), a substance known to induce the expression of virgenes of Agrobacterium and initiate processes leading to transformation,is added at a final concentration of 200 μM to Agrobacterium suspension,just before the cocultivation with maize shoots. The shoots are dippedinto Agrobacterium suspension and subjected to vacuum infiltration (-0.4to -0.6 Atm) for 5 min. The infiltrated maize shoots are culture on theagar plates of MS medium supplemented with 200 μM AS, in the phytotronunder the same condition as for germination of immature embryos. Theshoots are collected for GUS staining assay 3 days after cocultivationwith Agrobacterium.

16.4: Activity Assay for β-glucuronidase

Maize shoots are soaked with 0.052% 5-bromo-3-chloro-3-indolylglucuronide (X-Gluc) in 100 mM NaH₂ PO₄, pH 7.0, in the presence of 0.1%sodium azide. After 10 min of vacuum infiltration, the reactions arecontinued at 37° C. for two days in the dark. Shoots are destained forchlorophyll by rinsing with ethanol (70-90% ).

(D) RESULTS

A) Inoculation of 10-day-old Maize Plants

Table 1 shows the results of inoculation experiments on 10-day-old maizeplants described under point 10.1. The inoculation is carried out usingpEAP 37 DNA.

                  TABLE 1                                                         ______________________________________                                                number of plants with symptoms/                                         inoculation number of inoculated plants                                     site    pEAP 37     pMSV 109   pEAP 200                                                                             pEAP 25                                 ______________________________________                                        A        0/46 (<2%) --         -      -                                         B  0/44 (<2%) -- - -                                                          C  3/46 (6.5%) -- + +                                                         D 42/68 (62%) 26/65 (40%) ++ ++                                             ______________________________________                                    

The results in Table 1 show clearly that the preferred site odapplication on the plant is located in the region of the root collar,where 62% and 40% of the treated plants exhibit symptoms of infection,whilst the number of plants exhibiting symptoms of infection after beinginoculated at the other inoculation sites on the plant (A, B, C) is 0 ornegligibly small.

B) Inoculation of 3day-old Maize Seedlings

Tabel 2 shows the results of inoculation experiments on 3-day-old maizeseedlings described under point 10.2. The inoculation is carried outusing pEAP 37 and pEAP 40 DNA.

                  TABLE 2                                                         ______________________________________                                                     number of plants with symptoms/                                    inoculation number of inoculation plants                                    site         pEAP 37       pEAP 40                                            ______________________________________                                        E            21/27 (78%)   --                                                   F 0/20 (<5%) --                                                               G 3/19 (16%) --                                                               H 25/30 (83%) 51/58 (88%)                                                     I 8/51 (16%) --                                                               J 1/20 (5%) --                                                                K 2/12 (17%) --                                                             ______________________________________                                    

As the results in Table 2 show, the preferred site of application on themaize seedling is in the region of the coleoptile node, direct andindirect application of the bacterial suspension directly into thecoleoptile node, with 83% and 88% or 78% of the plants becominginfected, being clearly preferred by comparison with all otherapplication sites investigated. Whether the suspension is injecteddirectly into the coleoptile node laterally, or is injected indirectlythrough the coleoptile, is clearly of no significance.

C) Decapitation of 3-day-old Maize Seedlings

Table 3 shows the number of surviving seedlings 2 weeks afterdecapitation of the coleoptile at various sites in the region of thecoleoptile node.

                  TABLE 3                                                         ______________________________________                                        inoculation                                                                              number of surviving seedlings/                                       site number of decapitated seedlings                                        ______________________________________                                        1          0/7                                                                  2 5/8                                                                         3 8/8                                                                         4 8/8                                                                       ______________________________________                                    

It can be seen that the plumule can be removed up to 2 mm above thecoleoptile node without any impariment of the viability of the seedlingstreated in this manner being observed. Even removal of the plumul only 1mm above the coleoptile node still results in approximately 60% of casesin completely viable plantlets.

Table 4 shows the results of inoculation experiments on seedlingsdecapitated 2 mm above the coleoptile node. The inoculation is carriedout using pEAP 37 DNA.

                  TABLE 4                                                         ______________________________________                                        inoculation                                                                              number of plants with symptoms/                                      site number of inoculated plants                                            ______________________________________                                        L          48/49 (98%)                                                          M 14/44 (32%)                                                               ______________________________________                                    

The results in Table 4 show clearly that position L on the decapitatedseedling, that is to say the meristematic tissue region, is distinctlypreferred to position M, which covers the peripheral area of tissue.

D) Dilution Experiments

The bacterial suspension described under point 9 is diluted in YEBmedium without the addition of antibiotics and applied into thecoleoptilar node in the concentrations indicated below.

    ______________________________________                                               estimated number of                                                       bacteria remaining in number of plants with symptoms/                        dilution the inoculation site number of inoculated plants                   ______________________________________                                        undiluted                                                                            2 × 10.sup.6                                                                          84/102 (82%)                                               10.sup.-1 2 × 10.sup.5 42/55 (76%)                                      10.sup.-2 2 × 10.sup.4 34/54 (62%)                                      10.sup.-3 2 × 10.sup.3 19/56 (34%)                                      10.sup.-4 0 0/10 (<10%)                                                       10.sup.-5 0 0/10 (<10%)                                                     ______________________________________                                    

Assuming that the number of copies of the binary vector that containsthe MSV sequences is approximately 10 and that the bacteria do notincrease further in the inoculation site, 10⁴ bacteria containapproximately 400 fg (4×10¹³ g) of MSV-DNA.

This means that Agrobacterium transfers its DNA to maize with anefficiency comparable to that with which it transfers its DNA todicotyledonous host plants.

E) Agrobacterium Host Range

Apart from maize, it was possible to ascertain other representativesfrom the Gramineae class that are accessible to infection byAgrobacterium.

The results of inoculation experiments with these Gramineae species areshown in Table 5:

                  TABLE 5                                                         ______________________________________                                                         number of plants with symptoms/                                Gramineae species number of inoculated plants                               ______________________________________                                        barley (Maris Otter)                                                                           1/15 (6%)                                                      wheat (Maris Butler) 1/40 (2%)                                                wheat (normal) 1/25 (4%)                                                      spring oats (Saladin) 1/25 (4%)                                               Panicum milaceum 3/8 (35%)                                                    Digitaria sanguinalis 2/10 (20%)                                              Lolium temulentum 1/25 (4%)                                                 ______________________________________                                    

Some of the less effective results are possibly attributable totechnical difficulties arising in the course of inoculation, since theplants are in some cases very small and therefore have only small stemdiameters, which makes a specifically targeted injection of theinoculation solution difficult

This apart, the results above show that, besides maize, it is possibleto transform a number of other representatives from the Gramineae groupby means of Agrobacterium.

F) Agrobacterium Strains

In addition to the Agrobacterium tumefaciens strain C58 routinely usedin the inoculation experiments with maize, other A. tumefaciens and A.rhizogenes strains are also tested. It was also possible using thefollowing Agrobacterium stains listed in Table 6 to detect transfer ofMSV-DNA to maize:

                  TABLE 6                                                         ______________________________________                                                       number of plants with symptoms/                                  Agrobacterium number of inoculated plants                                   strain         pMSV 109 *1  pEAP 37 *2                                        ______________________________________                                        A. tumefaciens                                                                  T 37 3/6 (50%) 6/6 (100%)                                                     LBA 4301 (pTiC58) 21/23 (91%) 15/21 (71%)                                     A 6 0/8 (1%) 2/37 (5%)                                                        A. rhizogenes                                                                 R 1000 17/22 (81%) --                                                         LBA 9402 15/20 (75%) --                                                       2626 7/12 (51%) --                                                          ______________________________________                                         *1 The inoculation experiments with pMSV 109 are carried out on 10day-old     maize plants                                                                  *2 The inoculation experiments with pEAP 37 are carried out on 3day-old       maize seedlings.                                                         

                  TABLE 7                                                         ______________________________________                                        Agroinfection Frequencies* of Seedlings and In Vitro                            Germinated Mature Embryos                                                                  In Vitro-Germinated                                                                            3-Day-Old                                       Maize Line Excised Mature Embryos [%] Seedlings [%]                         ______________________________________                                        A188       81               90                                                  bx/bx 57 52                                                                   W23 33 53                                                                     880254A 53 30                                                               ______________________________________                                         *Frequencies of MSV symptom formation are determined 3 weeks after            inoculation by calculating the fraction of shoots showing MSV symptoms pe     total surviving (germinating) shoots.                                    

                                      TABLE 1                                     __________________________________________________________________________    Characteristics of Agrobacterium strains used for transformation of maize     Strain      Chromosome                                                                             Virulence genes   Binary vector                          __________________________________________________________________________    C58C1 (pBG5)                                                                              nopaline wild-type                                                                     none              GUS gene                                  C58C1  in pBIN19                                                             C58C1 (pTiC58, pBG5) id pTiC58: a nopaline wild-type Ti plasmid id                                                  C58C1 (pTiC58, pCG5) id id GUS                                               gene in                                     in pCGN1589.                                                               LBA4301 (pJK270, pCG5) octopine-type Ach5 pJK270 containing the full                                               set of C58 id                             derivative virulence genes                                                   LBA4301 (pJK190, pCG5) id pJK190, differing from pJK170, by a polar id                                                Tn5 insertion in vir B4                                                     LBA4301 (pJK210, pCG5) id pJK210,                                            differing from pJK270, by a non-                                              id                                         polar Tn5 insertion in vir B10                                            __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________    GUS expression detected on shoots of maize seedlings germinated from          immature embryos,                                                               after cultivation with Agrobactrium                                                              No. of                                                                            No. of shoots                                                                        % of shoots                                                                         Total no.                                                                          Average no.                            shoots showing showing of of blue spots                                     Agrobacterium maize tested blue spots blue spots blue spots per             __________________________________________________________________________                                               shoot                              A.                                                                              LBA4301 (pJK190, pCG5) A188, 14 DAP                                              5 DAG 41 13 32 266 6.4                                                        8 DAG 62 18 29 263 4.2                                                      K55, 14 DAP                                                                     5 DAG 54 0 0 0 0                                                           C58C1 (pBG5) A188, 14 DAP                                                        5 DAG 37 0 0 0 0                                                              8 DAG 60 0 0 0 0                                                           B.                                                                            C58C1 (pTiC58, pBG5) A188, 17 DAP                                                5 DAG 33 24 73 1031 31.2                                                 C58C1 (pTiC58, pCG5)                                                                      id       43  14     32    236  5.5                                  LBA4301 (pJK270, pCG5) id 54 7 13 96 1.8                                      LBA4301 (pJK190, pCG5) id 56 0 0 0 0                                          LBA4301 (pJK210, pCG5) id 55 0 0 0 0                                        __________________________________________________________________________     DAP: days after pollination; DAG: days after germination.                

(E) DEPOSITS

The plasmids used within the scope of the present invention, pEAP 37,pEAP 40 and pMSV 109, were deposited at the "Deutsche Sammlung vonMikroorganismen" (DSM), in Gottingen, Federal Republic of Germany and"The National Collection of Industrial Bacteria" (NCIB), Torry ResearchStation, P.O. Box 31, 135 Abbey Road, Aberdeen, both recognised asInternational Depositories in accordance with the requirements of theBudapest Treaty on the international recognition of the deposit ofmicroorganisms for the purposes of patent procedure. A declarationregarding the biability of the deposited samples was prepared by thesaid International Depositories.

    ______________________________________                                                   deposition deposition                                                                              date of the                                     microorganisms date number viability certificate                            ______________________________________                                        pEAP 37    16 June 1987                                                                             DSM 4147  19 June 1987                                    (Escherichia coli                                                             DH1 transformed                                                               with pEAP 37                                                                  plasmid-DNA)                                                                  pEAP 40 16 June 1987 DSM 4148 19 June 1987                                    (Escherichia coli                                                             DH1 transformed                                                               with pEAP 40                                                                  plasmid-DNA)                                                                  pMSV 109 23 Sept. 1987 NCIB 12547 24 Sept. 1987                               (Escherichia coli                                                             JM 83 RecA trans-                                                             formed with                                                                   pMSV 109                                                                      plasmid-DNA)                                                                ______________________________________                                    

Limitations on the availability of the said microorganisms have not beenrequested by the depositor.

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Patent Literature

WO 89/11291

WO 86/04356

WO 88/05826

US 4,810,777

WO 89/04371

EP-A 462,065

EP-A 392,225

What is claimed is:
 1. A transgenic monocotyledonous plant of theGramineae family obtained by a method for transforming plants withcloned viral DNA, wherein said cloned viral DNA, normally not infectiousupon mechanical inoculation, is amenable to transformation by a transfermicroorganism of the genus Agrobacterium, said method comprising:(a)inserting cloned viral DNA capable of giving rise to a systemicinfection and that may contain cargo DNA, into a T-replicon of anAgrobacterium, having one or more T-DNA border sequences, wherein thedistance between said cloned viral DNA and the T-DNA border sequences ischosen such that cloned viral DNA, including any cargo DNA present, isgenetically transferred to the plant material; (b) introducing theT-replicon into a transfer microorganism of the genus Agrobacterium, thereplicon passing into the transfer microorganism; (c) preparing amicroorganism-containing transforming suspension culture comprising thetransfer microorganism obtained in step (b); and (d) infecting plantmaterial with the transfer microorganism that has been modified inaccordance with step (b), said transgenic plant comprising in anexpressible form a chimaeric DNA construct comprising an expressible DNAin operable linkage with expression signals active in plant cells ofgraminaceous monocots.
 2. The transgenic plant according to claim 1,wherein said DNA further comprises coding sequences of the 5' region, 3'region, or 5' and 3' region.
 3. The transgenic plant according to claim1, wherein said DNA further comprises non-coding sequences of the 5'region, 3' region, or 5' and 3' region.
 4. The transgenic plantaccording to claim 1, wherein said expression signals are selected fromthe group consisting of promoter and termination sequences.
 5. Thetransgenic plant according to claim 1, which is a plant from one of thefollowing genera: Avena, Hordeum, Oryzae, Panicum, Saccharum, Secale,Setaria, Sorghum, Triticum, or Zea.
 6. The transgenic plant according toclaim 1, which is a maize plant.
 7. The transgenic plant according toclaim 1, wherein the T-replicon comprises more than one cloned viralDNA.
 8. The transgenic plant according to claim 7, wherein the clonedviral DNA is arranged in a tandemly duplicated form.
 9. The transgenicplant according to claim 1, wherein the cloned viral DNA is insertedbetween the T-DNA border sequences.
 10. The transgenic plant accordingto claim 1, wherein said cloned viral DNA is selected from the groupconsisting of(a) double-stranded DNA forms of single-stranded DNAviruses and functional parts thereof; (b) cDNA copies of viral RNA orviroid RNA and functional parts thereof; (c) any viable mutants ofviruses and functional parts thereof; and (d) portions of viral DNA thatare still capable of giving rise to a systemic infection.
 11. Thetransgenic plant according to claim 10, wherein the double-stranded DNAforms of single-stranded DNA viruses and functional parts thereof arefrom Gemini viruses.
 12. The transgenic plant according to claim 11,wherein said Gemini virus is a Maize Stroak Virus (MSV).
 13. Thetransgenic plant according to claim 1, wherein said expressible DNAcomprises a structural gene.
 14. The transgenic plant according to claim13, wherein said structural gene, upon expression, leads to a protectiveeffect in the transformed plant.
 15. A method according to claim 13,wherein said structural gene, upon expression, leads to resistanceagainst plant pathogens selected from the group consisting of insects,fungi, bacteria and viruses.
 16. The transgenic plant according to claim15, wherein said structural gene codes for a polypeptide that is toxicto insects or their larvae.
 17. The transgenic plant according to claim16, wherein said polypeptide is a crystalline protein of Bacillusthuringiensis.
 18. The transgenic plant according to claim 17, whereinsaid crystalline protein is encoded by a synthetic B.t. gene.
 19. Thetransgenic plant according to claim 15, wherein said structural genecodes for a lytic peptide.
 20. The transgenic plant according to claim15, wherein said structural gene codes for a pathogenesis relatedprotein.